l3 (10feb17)

git-svn-id: svn://tug.org/texlive/trunk@43183 c570f23f-e606-0410-a88d-b1316a301751

1 files changed, 862 insertions, 570 deletions

diff --git a/Master/texmf-dist/tex/latex/l3packages/xparse/xparse.sty b/Master/texmf-dist/tex/latex/l3packages/xparse/xparse.sty
index 8ac9148a45c..08e27c11845 100644
--- a/Master/texmf-dist/tex/latex/l3packages/xparse/xparse.sty
+++ b/Master/texmf-dist/tex/latex/l3packages/xparse/xparse.sty
@@ -22,9 +22,9 @@
 %%                      David Carlisle
 %%                  (C) Copyright 2004-2008 Frank Mittelbach,
 %%                      The LaTeX3 Project
-%%                  (C) Copyright 2009-2016 The LaTeX3 Project
-\RequirePackage{expl3}[2017/02/07]
-\@ifpackagelater{expl3}{2017/02/07}
+%%                  (C) Copyright 2009-2017 The LaTeX3 Project
+\RequirePackage{expl3}[2017/02/10]
+\@ifpackagelater{expl3}{2017/02/10}
   {}
   {%
     \PackageError{xparse}{Support package l3kernel too old}
@@ -38,22 +38,22 @@
   }
 \def\ExplFileName{xparse}
 \def\ExplFileDescription{L3 Experimental document command parser}
-\def\ExplFileDate{2017/02/07}
-\def\ExplFileVersion{6846}
+\def\ExplFileDate{2017/02/10}
+\def\ExplFileVersion{6878}
 \ProvidesExplPackage
   {\ExplFileName}{\ExplFileDate}{\ExplFileVersion}{\ExplFileDescription}
 \tl_const:Nx \c__xparse_no_value_tl
   { \char_generate:nn { `\- } { 11 } NoValue- }
-\prop_new:N \c__xparse_shorthands_prop
-\prop_put:Nnn \c__xparse_shorthands_prop { o } { d[] }
-\prop_put:Nnn \c__xparse_shorthands_prop { O } { D[] }
-\prop_put:Nnn \c__xparse_shorthands_prop { s } { t* }
 \bool_new:N \l__xparse_all_long_bool
+\bool_new:N \l__xparse_all_long_set_bool
+\tl_new:N \l__xparse_arg_spec_tl
 \tl_new:N \l__xparse_args_tl
-\prop_new:N \l__xparse_command_arg_specs_prop
+\tl_new:N \l__xparse_args_i_tl
+\tl_new:N \l__xparse_args_ii_tl
 \int_new:N \l__xparse_current_arg_int
+\bool_new:N \l__xparse_defaults_bool
+\tl_new:N \l__xparse_defaults_tl
 \bool_new:N \l__xparse_environment_bool
-\prop_new:N \l__xparse_environment_arg_specs_prop
 \bool_new:N \l__xparse_expandable_bool
 \tl_new:N \l__xparse_expandable_aux_name_tl
 \tl_set:Nn \l__xparse_expandable_aux_name_tl
@@ -61,17 +61,23 @@
     \l__xparse_function_tl \c_space_tl
     ( arg~ \int_use:N \l__xparse_current_arg_int )
   }
+\int_new:N \g__xparse_grabber_int
 \tl_new:N \l__xparse_fn_tl
+\tl_new:N \l__xparse_fn_code_tl
 \tl_new:N \l__xparse_function_tl
+\tl_new:N \l__xparse_last_delimiters_tl
 \bool_new:N \l__xparse_long_bool
 \int_new:N \l__xparse_m_args_int
 \int_new:N \l__xparse_mandatory_args_int
-\bool_new:N \l__xparse_processor_bool
-\int_new:N \l__xparse_processor_int
+\bool_new:N \l__xparse_prefixed_bool
+\tl_new:N \l__xparse_process_all_tl
+\tl_new:N \l__xparse_process_one_tl
+\bool_new:N \l__xparse_process_some_bool
 \tl_new:N \l__xparse_signature_tl
 \prop_new:N \l__xparse_tmp_prop
 \tl_new:N \l__xparse_tmpa_tl
 \tl_new:N \l__xparse_tmpb_tl
+\cs_new_eq:NN \__xparse_tmp:w ?
 \cs_new_protected:Npn \__xparse_declare_cmd:Nnn
   {
     \bool_set_false:N \l__xparse_expandable_bool
@@ -93,72 +99,70 @@
         \__msg_kernel_info:nnxx { xparse } { define-command }
           { \token_to_str:N #1 } { \tl_to_str:n {#2} }
       }
-    \prop_put:Nnn \l__xparse_command_arg_specs_prop {#1} {#2}
     \bool_set_false:N \l__xparse_environment_bool
     \__xparse_declare_cmd_internal:Nnn #1 {#2}
   }
 \cs_new_protected:Npn \__xparse_declare_cmd_internal:Nnn #1#2#3
   {
     \tl_set:Nx \l__xparse_function_tl { \cs_to_str:N #1 }
-    \__xparse_count_mandatory:n {#2}
-    \__xparse_prepare_signature:n {#2}
-    \int_compare:nNnTF \l__xparse_current_arg_int = \l__xparse_m_args_int
-      {
-        \bool_if:NTF \l__xparse_environment_bool
-          { \__xparse_declare_cmd_mixed:Nn #1 {#3} }
-          { \__xparse_declare_cmd_all_m:Nn #1 {#3} }
-      }
-      { \__xparse_declare_cmd_mixed:Nn #1 {#3} }
+    \__xparse_normalize_arg_spec:n {#2}
+    \exp_args:No \__xparse_prepare_signature:n \l__xparse_arg_spec_tl
+    \__xparse_declare_cmd_code:Nnn #1 {#2} {#3}
     \__xparse_break_point:n {#2}
   }
 \cs_generate_variant:Nn \__xparse_declare_cmd_internal:Nnn { cnx }
 \cs_new_eq:NN \__xparse_break_point:n \use_none:n
-\cs_new_protected:Npn \__xparse_declare_cmd_all_m:Nn #1#2
-  {
-    \cs_generate_from_arg_count:Ncnn #1
-      {
-        cs_set
-        \bool_if:NF \l__xparse_expandable_bool { _protected }
-        \bool_if:NF \l__xparse_all_long_bool { _nopar }
-        :Npn
-      }
-      \l__xparse_current_arg_int {#2}
-  }
-\cs_new_protected:Npn \__xparse_declare_cmd_mixed:Nn
+\cs_new_protected:Npn \__xparse_declare_cmd_code:Nnn
   {
     \bool_if:NTF \l__xparse_expandable_bool
-      { \__xparse_declare_cmd_mixed_expandable:Nn }
-      { \__xparse_declare_cmd_mixed_aux:Nn }
+      { \__xparse_declare_cmd_code_expandable:Nnn }
+      { \__xparse_declare_cmd_code_aux:Nnn }
    }
-\cs_new_protected:Npn \__xparse_declare_cmd_mixed_aux:Nn #1#2
+\cs_new_protected:Npn \__xparse_declare_cmd_code_aux:Nnn #1#2#3
   {
-    \__xparse_flush_m_args:
     \cs_generate_from_arg_count:cNnn
       { \l__xparse_function_tl \c_space_tl code }
-      \cs_set_protected:Npn \l__xparse_current_arg_int {#2}
+      \cs_set_protected:Npn \l__xparse_current_arg_int {#3}
     \cs_set_protected_nopar:Npx #1
       {
-        \int_zero:N \l__xparse_processor_int
-        \tl_set:Nn \exp_not:N \l__xparse_args_tl
-          { \exp_not:c { \l__xparse_function_tl \c_space_tl code } }
-        \tl_set:Nn \exp_not:N \l__xparse_fn_tl
-          { \exp_not:c { \l__xparse_function_tl \c_space_tl } }
-        \exp_not:o \l__xparse_signature_tl
-        \exp_not:N \l__xparse_args_tl
+        \__xparse_start:nNNnnn
+          { \exp_not:n {#2} }
+          \exp_not:c { \l__xparse_function_tl \c_space_tl }
+          \exp_not:c { \l__xparse_function_tl \c_space_tl code }
+          { \exp_not:o \l__xparse_signature_tl }
+          {
+            \bool_if:NT \l__xparse_defaults_bool
+              { \exp_not:o \l__xparse_defaults_tl }
+          }
+          {
+            \bool_if:NT \l__xparse_process_some_bool
+              { \exp_not:o \l__xparse_process_all_tl }
+          }
       }
   }
-\cs_new_protected:Npn \__xparse_declare_cmd_mixed_expandable:Nn #1#2
+\cs_new_protected:Npn \__xparse_declare_cmd_code_expandable:Nnn #1#2#3
   {
     \cs_generate_from_arg_count:cNnn
       { \l__xparse_function_tl \c_space_tl code }
-      \cs_set:Npn \l__xparse_current_arg_int {#2}
+      \cs_set:Npn \l__xparse_current_arg_int {#3}
+    \bool_if:NT \l__xparse_defaults_bool
+      {
+        \use:x
+          {
+            \cs_generate_from_arg_count:cNnn
+              { \l__xparse_function_tl \c_space_tl defaults }
+              \cs_set:Npn \l__xparse_current_arg_int
+              { \exp_not:o \l__xparse_defaults_tl }
+          }
+      }
     \cs_set_nopar:Npx #1
       {
-        \exp_not:o \l__xparse_signature_tl
-        \exp_not:N \__xparse_grab_expandable_end:wN
-        \exp_not:c { \l__xparse_function_tl \c_space_tl code }
-        \exp_not:N \q__xparse
-        \exp_not:c { \l__xparse_function_tl \c_space_tl }
+        \exp_not:N \__xparse_start_expandable:nNNNn
+          { \exp_not:n {#2} }
+          \exp_not:c { \l__xparse_function_tl \c_space_tl }
+          \exp_not:c { \l__xparse_function_tl \c_space_tl code }
+          \exp_not:c { \l__xparse_function_tl \c_space_tl defaults }
+          { \exp_not:o \l__xparse_signature_tl }
       }
     \bool_if:NTF \l__xparse_all_long_bool
       { \cs_set:cpx }
@@ -176,7 +180,6 @@
         \__msg_kernel_info:nnxx { xparse } { define-environment }
           {#1} { \tl_to_str:n {#2} }
       }
-    \prop_put:Nnn \l__xparse_environment_arg_specs_prop {#1} {#2}
     \bool_set_false:N \l__xparse_expandable_bool
     \bool_set_true:N \l__xparse_environment_bool
     \__xparse_declare_env_internal:nnnn {#1} {#2}
@@ -188,7 +191,7 @@
         \cs_set_nopar:Npx \exp_not:c { environment~ #1 ~end~aux }
           {
             \exp_not:N \exp_not:N \exp_not:c { environment~ #1~end~aux~ }
-            \exp_not:n { \tl_tail:N \l__xparse_args_tl }
+            \exp_not:n { \exp_not:o \l__xparse_args_tl }
           }
         \exp_not:n {#3}
       }
@@ -200,222 +203,467 @@
     \cs_set_eq:cc {#1}       { environment~ #1 }
     \cs_set_eq:cc { end #1 } { environment~ #1 ~end }
   }
-\cs_new_protected:Npn \__xparse_count_mandatory:n #1
+\cs_new_protected:Npn \__xparse_start:nNNnnn #1#2#3#4#5#6
+  {
+    \tl_clear:N \l__xparse_args_tl
+    \tl_set:Nn \l__xparse_fn_tl {#2}
+    \tl_set:Nn \l__xparse_fn_code_tl {#3}
+    \tl_set:Nn \l__xparse_defaults_tl {#5}
+    \tl_set:Nn \l__xparse_process_all_tl {#6}
+    #4 \__xparse_run_code:
+  }
+\cs_new_protected:Npn \__xparse_run_code:
+  {
+    \tl_if_empty:NF \l__xparse_defaults_tl { \__xparse_defaults: }
+    \tl_if_empty:NF \l__xparse_process_all_tl { \__xparse_args_process: }
+    \exp_after:wN \l__xparse_fn_code_tl \l__xparse_args_tl
+  }
+\cs_new_protected:Npn \__xparse_defaults:
+  {
+    \__xparse_defaults_def:
+    \tl_set_eq:NN \l__xparse_args_i_tl \l__xparse_args_tl
+    \__xparse_defaults_aux: \__xparse_defaults_aux: \__xparse_defaults_aux:
+    \__xparse_defaults_aux: \__xparse_defaults_aux: \__xparse_defaults_aux:
+    \__xparse_defaults_aux: \__xparse_defaults_aux: \__xparse_defaults_aux:
+    \__xparse_defaults_error:w
+    \q_recursion_stop
+    \tl_set_eq:NN \l__xparse_args_tl \l__xparse_args_i_tl
+  }
+\cs_new_protected:Npn \__xparse_defaults_aux:
+  {
+    \tl_set:Nx \l__xparse_args_ii_tl
+      { \exp_after:wN \__xparse_tmp:w \l__xparse_args_i_tl }
+    \tl_if_eq:NNT \l__xparse_args_ii_tl \l__xparse_args_i_tl
+      { \use_none_delimit_by_q_recursion_stop:w }
+    \tl_set_eq:NN \l__xparse_args_i_tl \l__xparse_args_ii_tl
+  }
+\cs_new_protected:Npn \__xparse_defaults_error:w \q_recursion_stop
+  {
+    \__msg_kernel_error:nnx { xparse } { loop-in-defaults }
+      { \exp_after:wN \token_to_str:N \l__xparse_fn_tl }
+  }
+\cs_new_protected:Npn \__xparse_defaults_def:
+  {
+    \tl_clear:N \l__xparse_tmpa_tl
+    \int_zero:N \l__xparse_current_arg_int
+    \__xparse_tl_mapthread_function:NNN \l__xparse_args_tl \l__xparse_defaults_tl
+      \__xparse_defaults_def:nn
+    \cs_generate_from_arg_count:NNVo \__xparse_tmp:w \cs_set:Npn
+      \l__xparse_current_arg_int \l__xparse_tmpa_tl
+  }
+\cs_generate_variant:Nn \cs_generate_from_arg_count:NNnn { NNVo }
+\cs_new_protected:Npn \__xparse_defaults_def:nn
+  {
+    \int_incr:N \l__xparse_current_arg_int
+    \exp_args:NV \__xparse_defaults_def:nnn \l__xparse_current_arg_int
+  }
+\cs_new_protected:Npn \__xparse_defaults_def:nnn #1#2#3
+  {
+    \tl_if_head_is_group:nTF {#3}
+      {
+        \tl_put_right:Nn \l__xparse_tmpa_tl
+          {
+            {
+              \exp_args:Nf \__xparse_tl_mapthread_function:nnN
+                { \tl_item:Nn \l__xparse_args_tl {#1} }
+                {#3}
+                \__xparse_defaults_def_aux:nn
+            }
+          }
+      }
+      {
+        \__xparse_if_no_value:nTF {#2}
+          {
+            \tl_put_right:Nx \l__xparse_tmpa_tl
+              { { \exp_not:N \exp_not:n { \exp_not:o { \use_none:n #3 } } } }
+          }
+          {
+            \tl_put_right:Nn \l__xparse_tmpa_tl
+              { { \exp_not:n { ## #1 } } }
+          }
+      }
+  }
+\cs_new:Npn \__xparse_defaults_def_aux:nn #1#2
+  {
+    \__xparse_if_no_value:nTF {#1}
+      { { \exp_not:n {#2} } }
+      { { \exp_not:n {#1} } }
+  }
+\cs_new_protected:Npn \__xparse_args_process:
+  {
+    \tl_clear:N \l__xparse_args_ii_tl
+    \__xparse_tl_mapthread_function:NNN
+      \l__xparse_args_tl
+      \l__xparse_process_all_tl
+      \__xparse_args_process_loop:nn
+    \tl_set_eq:NN \l__xparse_args_tl \l__xparse_args_ii_tl
+  }
+\cs_new_protected:Npn \__xparse_args_process_loop:nn #1#2
+  {
+    \tl_set:Nn \ProcessedArgument {#1}
+    \__xparse_if_no_value:nF {#1}
+      { \tl_map_function:nN {#2} \__xparse_args_process_aux:n }
+    \tl_put_right:No \l__xparse_args_ii_tl
+      { \exp_after:wN { \ProcessedArgument } }
+  }
+\cs_new_protected:Npn \__xparse_args_process_aux:n
+  { \exp_args:No \__xparse_args_process_aux:nn { \ProcessedArgument } }
+\cs_new_protected:Npn \__xparse_args_process_aux:nn #1#2 { #2 {#1} }
+\cs_new:Npn \__xparse_start_expandable:nNNNn #1#2#3#4#5
+  { #5 \__xparse_end_expandable:NNw #4 #3 \q__xparse #2 }
+\cs_new:Npn \__xparse_end_expandable:NNw #1#2
+  { \__xparse_end_expandable_aux:w #1#2 \prg_do_nothing: }
+\cs_new:Npn \__xparse_end_expandable_aux:w #1#2#3 \q__xparse #4
+  { \exp_args:No \__xparse_end_expandable_aux:nNNN {#3} #1 #2 #4 }
+\cs_new:Npn \__xparse_end_expandable_aux:nNNN #1#2#3#4
+  {
+    \cs_if_exist:NF #2 { \exp_after:wN \use_iv:nnnn }
+    \__xparse_end_expandable_defaults:nnnNNn {#1} { } {#1} #2#3
+      { } { } { } { } { } { } { } { } { } { }
+      {
+        \__msg_kernel_expandable_error:nnn
+          { xparse } { loop-in-defaults } {#4}
+        \use_iv:nnnn
+      }
+    \q_stop
+  }
+\cs_new:Npn \__xparse_end_expandable_defaults:nnnNNn #1#2#3#4#5#6
+  {
+    #6
+    \str_if_eq:nnTF {#1} {#2}
+      { \use_i_delimit_by_q_stop:nw { #5 #1 } }
+      {
+        \exp_args:No \__xparse_tl_mapthread_function:nnN
+          { #4 #1 } {#3}
+          \__xparse_end_expandable_defaults:nnw
+        \__xparse_end_expandable_defaults:nnnNNn { } {#1} {#3} #4 #5
+      }
+  }
+\cs_new:Npn \__xparse_end_expandable_defaults:nnw #1#2
+  {
+    \tl_if_head_is_group:nTF {#1}
+      {
+        \__xparse_end_expandable_defaults_E:nnw { }
+          #1 \q_nil \q_mark
+          #2 \q_nil
+      }
+      {
+        \__xparse_if_no_value:nTF {#2}
+          { \exp_args:No \__xparse_end_expandable_defaults:nw { \use_none:n #1 } }
+          { \__xparse_end_expandable_defaults:nw {#2} }
+      }
+  }
+\cs_new:Npn \__xparse_end_expandable_defaults_E:nnw #1#2#3 \q_mark #4
+  {
+    \quark_if_nil:nTF {#2}
+      { \__xparse_end_expandable_defaults:nw {#1} }
+      {
+        \__xparse_if_no_value:nTF {#4}
+          { \__xparse_end_expandable_defaults_E:nnw { #1 {#2} } }
+          { \__xparse_end_expandable_defaults_E:nnw { #1 {#4} } }
+        #3 \q_mark
+      }
+  }
+\cs_new:Npn \__xparse_end_expandable_defaults:nw
+    #1#2 \__xparse_end_expandable_defaults:nnnNNn #3
+  { #2 \__xparse_end_expandable_defaults:nnnNNn { #3 {#1} } }
+\cs_new_protected:Npn \__xparse_normalize_arg_spec:n #1
   {
     \int_zero:N \l__xparse_mandatory_args_int
-    \__xparse_count_mandatory:N #1
+    \int_zero:N \l__xparse_current_arg_int
+    \tl_clear:N \l__xparse_last_delimiters_tl
+    \tl_clear:N \l__xparse_arg_spec_tl
+    \__xparse_normalize_arg_spec_loop:n #1
       \q_recursion_tail \q_recursion_tail \q_recursion_tail \q_recursion_stop
+    \int_compare:nNnT \l__xparse_current_arg_int > 9
+      {
+        \__msg_kernel_error:nnxx { xparse } { too-many-arguments }
+          { \iow_char:N \\ \l__xparse_function_tl } { \tl_to_str:n {#1} }
+        \__xparse_bad_def:wn
+      }
+    \bool_if:NT \l__xparse_expandable_bool
+      {
+        \tl_if_empty:NF \l__xparse_last_delimiters_tl
+          {
+            \__msg_kernel_error:nnxx { xparse } { expandable-ending-optional }
+              { \iow_char:N \\ \l__xparse_function_tl } { \tl_to_str:n {#1} }
+            \__xparse_bad_def:wn
+          }
+      }
   }
-\cs_new_protected:Npn \__xparse_count_mandatory:N #1
+\cs_new_protected:Npn \__xparse_normalize_arg_spec_loop:n #1
   {
-    \quark_if_recursion_tail_stop:N #1
-    \prop_get:NnNTF \c__xparse_shorthands_prop {#1} \l__xparse_tmpa_tl
-      { \exp_after:wN \__xparse_count_mandatory:N \l__xparse_tmpa_tl }
-      { \__xparse_count_mandatory_aux:N #1 }
+    \quark_if_recursion_tail_stop:n {#1}
+    \int_incr:N \l__xparse_current_arg_int
+    \cs_if_exist_use:cF { __xparse_normalize_type_ \tl_to_str:n {#1} :w }
+      {
+        \__msg_kernel_error:nnxx { xparse } { unknown-argument-type }
+          { \iow_char:N \\ \l__xparse_function_tl } { \tl_to_str:n {#1} }
+        \__xparse_bad_def:wn
+      }
   }
-\cs_new_protected:Npn \__xparse_count_mandatory_aux:N #1
+\cs_set_protected:Npn \__xparse_tmp:w #1
   {
-    \cs_if_exist_use:cF { __xparse_count_type_ \token_to_str:N #1 :w }
-      { \__xparse_count_type_m:w }
+    \cs_new_protected:Npn \__xparse_normalize_type_d:w ##1##2
+      {
+        \quark_if_recursion_tail_stop_do:nn {##2} { \__xparse_bad_arg_spec:wn }
+        \__xparse_normalize_type_D:w {##1} {##2} {#1}
+      }
+    \cs_new_protected:Npn \__xparse_normalize_type_e:w ##1
+      {
+        \quark_if_recursion_tail_stop_do:nn {##1} { \__xparse_bad_arg_spec:wn }
+        \__xparse_normalize_type_E:w {##1} { }
+      }
+    \cs_new_protected:Npn \__xparse_normalize_type_g:w
+      { \__xparse_normalize_type_G:w {#1} }
+    \cs_new_protected:Npn \__xparse_normalize_type_o:w
+      { \__xparse_normalize_type_D:w [ ] {#1} }
+    \cs_new_protected:Npn \__xparse_normalize_type_O:w
+      { \__xparse_normalize_type_D:w [ ] }
+    \cs_new_protected:Npn \__xparse_normalize_type_r:w ##1##2
+      {
+        \quark_if_recursion_tail_stop_do:nn {##2} { \__xparse_bad_arg_spec:wn }
+        \__xparse_normalize_type_R:w {##1} {##2} {#1}
+      }
+    \cs_new_protected:Npn \__xparse_normalize_type_s:w
+      { \__xparse_normalize_type_t:w * }
   }
-\cs_new_protected:cpn { __xparse_count_type_>:w } #1#2
+\exp_args:No \__xparse_tmp:w { \c__xparse_no_value_tl }
+\cs_new_protected:cpn { __xparse_normalize_type_>:w } #1#2
   {
     \quark_if_recursion_tail_stop_do:nn {#2} { \__xparse_bad_arg_spec:wn }
-    \__xparse_count_mandatory:N #2
+    \bool_if:NT \l__xparse_expandable_bool
+      {
+        \__msg_kernel_error:nnxx { xparse } { processor-in-expandable }
+          { \iow_char:N \\ \l__xparse_function_tl } { \tl_to_str:n {#1} }
+        \__xparse_bad_def:wn
+      }
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { > {#1} }
+    \int_decr:N \l__xparse_current_arg_int
+    \__xparse_normalize_arg_spec_loop:n {#2}
   }
-\cs_new_protected:cpn { __xparse_count_type_+:w } #1
+\cs_new_protected:cpn { __xparse_normalize_type_+:w } #1
   {
     \quark_if_recursion_tail_stop_do:nn {#1} { \__xparse_bad_arg_spec:wn }
-    \__xparse_count_mandatory:N #1
-  }
-\cs_new_protected:Npn \__xparse_count_type_d:w #1#2
-  {
-    \__xparse_single_token_check:n {#1}
-    \__xparse_single_token_check:n {#2}
-    \quark_if_recursion_tail_stop_do:Nn #2 { \__xparse_bad_arg_spec:wn }
-    \__xparse_count_mandatory:N
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { + }
+    \int_decr:N \l__xparse_current_arg_int
+    \__xparse_normalize_arg_spec_loop:n {#1}
   }
-\cs_new_protected:Npn \__xparse_count_type_D:w #1#2#3
+\cs_new_protected:Npn \__xparse_normalize_type_D:w #1#2#3
   {
     \__xparse_single_token_check:n {#1}
     \__xparse_single_token_check:n {#2}
     \quark_if_recursion_tail_stop_do:nn {#3} { \__xparse_bad_arg_spec:wn }
-    \__xparse_count_mandatory:N
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { D #1 #2 {#3} }
+    \tl_put_right:Nn \l__xparse_last_delimiters_tl {#1}
+    \__xparse_normalize_arg_spec_loop:n
   }
-\cs_new_protected:Npn \__xparse_count_type_e:w #1
-  {
-    \quark_if_recursion_tail_stop_do:nn {#1} { \__xparse_bad_arg_spec:wn }
-    \__xparse_count_mandatory:N
-  }
-\cs_new_protected:Npn \__xparse_count_type_E:w #1#2
+\cs_new_protected:Npn \__xparse_normalize_type_E:w #1#2
   {
     \quark_if_recursion_tail_stop_do:nn {#2} { \__xparse_bad_arg_spec:wn }
-    \__xparse_count_mandatory:N
+    \tl_if_blank:nT {#1} { \__xparse_bad_arg_spec:wn }
+    \tl_map_function:nN {#1} \__xparse_single_token_check:n
+    \int_compare:nNnT { \tl_count:n {#2} } > { \tl_count:n {#1} }
+      { \__xparse_bad_arg_spec:wn }
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { E {#1} {#2} }
+    \tl_put_right:Nn \l__xparse_last_delimiters_tl {#1}
+    \__xparse_normalize_arg_spec_loop:n
   }
-\cs_new_protected:Npn \__xparse_count_type_g:w
-  { \__xparse_count_mandatory:N }
-\cs_new_protected:Npn \__xparse_count_type_G:w #1
+\cs_new_protected:Npn \__xparse_normalize_type_G:w #1
   {
     \quark_if_recursion_tail_stop_do:nn {#1} { \__xparse_bad_arg_spec:wn }
-    \__xparse_count_mandatory:N
+    \__xparse_normalize_error_if_expandable:N G
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { G {#1} }
+    \tl_put_right:Nn \l__xparse_last_delimiters_tl { { } }
+    \__xparse_normalize_arg_spec_loop:n
+  }
+\cs_new_protected:Npn \__xparse_normalize_type_t:w #1
+  {
+    \__xparse_single_token_check:n {#1}
+    \quark_if_recursion_tail_stop_do:Nn #1 { \__xparse_bad_arg_spec:wn }
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { t #1 }
+    \tl_put_right:Nn \l__xparse_last_delimiters_tl {#1}
+    \__xparse_normalize_arg_spec_loop:n
   }
-\cs_new_protected:Npn \__xparse_count_type_m:w
+\cs_new_protected:Npn \__xparse_normalize_type_l:w
   {
+    \__xparse_normalize_error_if_expandable:N l
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { l }
     \int_incr:N \l__xparse_mandatory_args_int
-    \__xparse_count_mandatory:N
+    \tl_clear:N \l__xparse_last_delimiters_tl
+    \__xparse_normalize_arg_spec_loop:n
   }
-\cs_new_protected:Npn \__xparse_count_type_r:w #1#2
+\cs_new_protected:Npn \__xparse_normalize_type_m:w
   {
-    \__xparse_single_token_check:n {#1}
-    \__xparse_single_token_check:n {#2}
-    \quark_if_recursion_tail_stop_do:Nn #2 { \__xparse_bad_arg_spec:wn }
+    \__xparse_delimiter_check:nnn { } { m } { \iow_char:N \{ }
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { m }
     \int_incr:N \l__xparse_mandatory_args_int
-    \__xparse_count_mandatory:N
+    \tl_clear:N \l__xparse_last_delimiters_tl
+    \__xparse_normalize_arg_spec_loop:n
   }
-\cs_new_protected:Npn \__xparse_count_type_R:w #1#2#3
+\cs_new_protected:Npn \__xparse_normalize_type_R:w #1#2#3
   {
     \__xparse_single_token_check:n {#1}
     \__xparse_single_token_check:n {#2}
     \quark_if_recursion_tail_stop_do:nn {#3} { \__xparse_bad_arg_spec:wn }
+    \__xparse_delimiter_check:nnn {#1} { R/r } { \tl_to_str:n {#1} }
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { R #1 #2 {#3} }
     \int_incr:N \l__xparse_mandatory_args_int
-    \__xparse_count_mandatory:N
+    \tl_clear:N \l__xparse_last_delimiters_tl
+    \__xparse_normalize_arg_spec_loop:n
   }
-\cs_new_protected:Npn \__xparse_count_type_t:w #1
+\cs_new_protected:Npn \__xparse_normalize_type_u:w #1
   {
-    \__xparse_single_token_check:n {#1}
-    \quark_if_recursion_tail_stop_do:Nn #1 { \__xparse_bad_arg_spec:wn }
-    \__xparse_count_mandatory:N
+    \quark_if_recursion_tail_stop_do:nn {#1} { \__xparse_bad_arg_spec:wn }
+    \__xparse_normalize_error_if_expandable:N u
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { u {#1} }
+    \int_incr:N \l__xparse_mandatory_args_int
+    \tl_clear:N \l__xparse_last_delimiters_tl
+    \__xparse_normalize_arg_spec_loop:n
   }
-\cs_new_protected:Npn \__xparse_count_type_u:w #1
+\cs_new_protected:Npn \__xparse_normalize_type_v:w
   {
-    \quark_if_recursion_tail_stop_do:nn {#1} { \__xparse_bad_arg_spec:wn }
+    \__xparse_normalize_error_if_expandable:N v
+    \tl_put_right:Nn \l__xparse_arg_spec_tl { v }
     \int_incr:N \l__xparse_mandatory_args_int
-    \__xparse_count_mandatory:N
+    \tl_clear:N \l__xparse_last_delimiters_tl
+    \__xparse_normalize_arg_spec_loop:n
   }
 \cs_new_protected:Npn \__xparse_single_token_check:n #1
   {
     \exp_args:Nx \tl_if_single_token:nF { \tl_trim_spaces:n {#1} }
-      { \__xparse_single_token_check_aux:nwn {#1} }
+      {
+        \__msg_kernel_error:nnxx { xparse } { not-single-token }
+          { \iow_char:N \\ \l__xparse_function_tl } { \tl_to_str:n {#1} }
+        \__xparse_bad_def:wn
+      }
   }
-\cs_new_protected:Npn \__xparse_single_token_check_aux:nwn
-  #1#2 \__xparse_break_point:n #3
+\cs_new_protected:Npn \__xparse_normalize_error_if_expandable:N #1
   {
-    \__msg_kernel_error:nnx { xparse } { not-single-token }
-      { \tl_to_str:n {#1} } { \tl_to_str:n {#3} }
+    \bool_if:NT \l__xparse_expandable_bool
+      {
+        \__msg_kernel_error:nnxx
+          { xparse } { invalid-expandable-argument-type }
+          { \iow_char:N \\ \l__xparse_function_tl } { \tl_to_str:n {#1} }
+        \__xparse_bad_def:wn
+      }
+  }
+\cs_new_protected:Npn \__xparse_delimiter_check:nnn #1#2#3
+  {
+    \tl_map_inline:Nn \l__xparse_last_delimiters_tl
+      {
+        \tl_if_eq:nnT {##1} {#1}
+          {
+            \__msg_kernel_warning:nnxx { xparse } { optional-mandatory }
+              {#2} {#3}
+          }
+      }
   }
 \cs_new_protected:Npn \__xparse_bad_arg_spec:wn #1 \__xparse_break_point:n #2
-  { \__msg_kernel_error:nnx { xparse } { bad-arg-spec } { \tl_to_str:n {#2} } }
+  {
+    \__msg_kernel_error:nnxx { xparse } { bad-arg-spec }
+      { \iow_char:N \\ \l__xparse_function_tl } { \tl_to_str:n {#2} }
+  }
+\cs_new_protected:Npn \__xparse_bad_def:wn #1 \__xparse_break_point:n #2 { }
 \cs_new_protected:Npn \__xparse_prepare_signature:n #1
   {
     \bool_set_false:N \l__xparse_all_long_bool
+    \bool_set_false:N \l__xparse_all_long_set_bool
     \int_zero:N \l__xparse_current_arg_int
     \bool_set_false:N \l__xparse_long_bool
     \int_zero:N \l__xparse_m_args_int
-    \bool_set_false:N \l__xparse_processor_bool
+    \bool_set_false:N \l__xparse_defaults_bool
+    \tl_clear:N \l__xparse_defaults_tl
+    \tl_clear:N \l__xparse_process_all_tl
+    \tl_clear:N \l__xparse_process_one_tl
+    \bool_set_false:N \l__xparse_process_some_bool
     \tl_clear:N \l__xparse_signature_tl
     \__xparse_prepare_signature:N #1 \q_recursion_tail \q_recursion_stop
+    \bool_if:NF \l__xparse_expandable_bool { \__xparse_flush_m_args: }
   }
 \cs_new_protected:Npn \__xparse_prepare_signature:N
   {
-    \bool_set_false:N \l__xparse_processor_bool
+    \bool_set_false:N \l__xparse_prefixed_bool
     \__xparse_prepare_signature_bypass:N
   }
 \cs_new_protected:Npn \__xparse_prepare_signature_bypass:N #1
   {
     \quark_if_recursion_tail_stop:N #1
-    \prop_get:NnNTF \c__xparse_shorthands_prop {#1} \l__xparse_tmpa_tl
-      { \exp_after:wN \__xparse_prepare_signature:N \l__xparse_tmpa_tl }
-      {
-        \int_incr:N \l__xparse_current_arg_int
-        \__xparse_prepare_signature_add:N #1
-      }
-  }
-\cs_new_protected:Npn \__xparse_prepare_signature_add:N #1
-  {
-    \cs_if_exist_use:cF
+    \int_incr:N \l__xparse_current_arg_int
+    \use:c
       {
          __xparse_add
          \bool_if:NT \l__xparse_expandable_bool { _expandable }
          _type_  \token_to_str:N #1 :w
       }
-      {
-        \__msg_kernel_error:nnx { xparse } { unknown-argument-type }
-          { \token_to_str:N #1 }
-        \bool_if:NTF \l__xparse_expandable_bool
-          { \__xparse_add_expandable_type_m:w }
-          { \__xparse_add_type_m:w }
-      }
   }
 \cs_new_protected:cpn { __xparse_add_type_+:w }
   {
     \__xparse_flush_m_args:
     \bool_set_true:N \l__xparse_long_bool
+    \bool_set_true:N \l__xparse_prefixed_bool
     \int_decr:N \l__xparse_current_arg_int
-    \__xparse_prepare_signature:N
+    \__xparse_prepare_signature_bypass:N
   }
 \cs_new_protected:cpn { __xparse_add_type_>:w } #1
   {
     \__xparse_flush_m_args:
-    \bool_set_true:N \l__xparse_processor_bool
+    \bool_set_true:N \l__xparse_prefixed_bool
+    \bool_set_true:N \l__xparse_process_some_bool
     \int_decr:N \l__xparse_current_arg_int
-    \tl_put_right:Nn \l__xparse_signature_tl { \__xparse_process_arg:n {#1} }
+    \tl_put_right:Nn \l__xparse_process_one_tl { {#1} }
     \__xparse_prepare_signature_bypass:N
   }
-\cs_new_protected:Npn \__xparse_add_type_d:w #1#2
-  { \exp_args:NNNo \__xparse_add_type_D:w #1 #2 \c__xparse_no_value_tl }
 \cs_new_protected:Npn \__xparse_add_type_D:w #1#2#3
   {
     \__xparse_flush_m_args:
+    \__xparse_add_default:n {#3}
     \__xparse_add_grabber_optional:N D
-    \tl_put_right:Nn \l__xparse_signature_tl { #1 #2 {#3} }
+    \tl_put_right:Nn \l__xparse_signature_tl { #1 #2 }
     \__xparse_prepare_signature:N
   }
-\cs_new_protected:Npn \__xparse_add_type_e:w #1
-  { \__xparse_add_type_E:w {#1} { } }
 \cs_new_protected:Npn \__xparse_add_type_E:w #1#2
   {
     \__xparse_flush_m_args:
+    \__xparse_add_default_E:nn {#1} {#2}
     \__xparse_add_grabber_optional:N E
-    \tl_put_right:Nn \l__xparse_signature_tl { {#1} {#2} }
+    \tl_put_right:Nn \l__xparse_signature_tl { {#1} }
     \__xparse_prepare_signature:N
   }
-\cs_new_protected:Npn \__xparse_add_type_g:w
-  { \exp_args:No \__xparse_add_type_G:w \c__xparse_no_value_tl }
 \cs_new_protected:Npn \__xparse_add_type_G:w #1
   {
     \__xparse_flush_m_args:
+    \__xparse_add_default:n {#1}
     \__xparse_add_grabber_optional:N G
-    \tl_put_right:Nn \l__xparse_signature_tl { {#1} }
     \__xparse_prepare_signature:N
   }
 \cs_new_protected:Npn \__xparse_add_type_l:w
   {
     \__xparse_flush_m_args:
+    \__xparse_add_default:
     \__xparse_add_grabber_mandatory:N l
     \__xparse_prepare_signature:N
   }
 \cs_new_protected:Npn \__xparse_add_type_m:w
   {
-    \bool_if:nTF { \l__xparse_long_bool || \l__xparse_processor_bool }
-      {
-        \__xparse_flush_m_args:
-        \__xparse_add_grabber_mandatory:N m
-      }
+    \__xparse_add_default:
+    \bool_if:NTF \l__xparse_prefixed_bool
+      { \__xparse_add_grabber_mandatory:N m }
       { \int_incr:N \l__xparse_m_args_int }
     \__xparse_prepare_signature:N
   }
-\cs_new_protected:Npn \__xparse_add_type_r:w #1#2
-  { \exp_args:NNNo \__xparse_add_type_R:w #1 #2 \c__xparse_no_value_tl }
 \cs_new_protected:Npn \__xparse_add_type_R:w #1#2#3
   {
     \__xparse_flush_m_args:
+    \__xparse_add_default:n {#3}
     \__xparse_add_grabber_mandatory:N R
-    \tl_put_right:Nn \l__xparse_signature_tl { #1 #2 {#3} }
+    \tl_put_right:Nn \l__xparse_signature_tl { #1 #2 }
     \__xparse_prepare_signature:N
   }
 \cs_new_protected:Npn \__xparse_add_type_t:w #1
   {
     \__xparse_flush_m_args:
+    \__xparse_add_default:
     \__xparse_add_grabber_optional:N t
     \tl_put_right:Nn \l__xparse_signature_tl {#1}
     \__xparse_prepare_signature:N
@@ -423,6 +671,7 @@
 \cs_new_protected:Npn \__xparse_add_type_u:w #1
   {
     \__xparse_flush_m_args:
+    \__xparse_add_default:
     \__xparse_add_grabber_mandatory:N u
     \tl_put_right:Nn \l__xparse_signature_tl { {#1} }
     \__xparse_prepare_signature:N
@@ -430,6 +679,7 @@
 \cs_new_protected:Npn \__xparse_add_type_v:w
   {
     \__xparse_flush_m_args:
+    \exp_args:No \__xparse_add_default:n \c__xparse_no_value_tl
     \__xparse_add_grabber_mandatory:N v
     \__xparse_prepare_signature:N
   }
@@ -440,6 +690,8 @@
         \tl_put_right:Nx \l__xparse_signature_tl
           { \exp_not:c { __xparse_grab_m_ \int_use:N \l__xparse_m_args_int :w } }
         \int_sub:Nn \l__xparse_mandatory_args_int { \l__xparse_m_args_int }
+        \tl_put_right:Nx \l__xparse_process_all_tl
+          { \prg_replicate:nn { \l__xparse_m_args_int } { { } } }
       }
     \int_zero:N \l__xparse_m_args_int
   }
@@ -451,6 +703,9 @@
           { __xparse_grab_ #1 \bool_if:NT \l__xparse_long_bool { _long } :w }
       }
     \bool_set_false:N \l__xparse_long_bool
+    \tl_put_right:Nx \l__xparse_process_all_tl
+      { { \exp_not:o \l__xparse_process_one_tl } }
+    \tl_clear:N \l__xparse_process_one_tl
     \int_decr:N \l__xparse_mandatory_args_int
   }
 \cs_new_protected:Npn \__xparse_add_grabber_optional:N #1
@@ -467,231 +722,229 @@
           }
       }
     \bool_set_false:N \l__xparse_long_bool
+    \tl_put_right:Nx \l__xparse_process_all_tl
+      { { \exp_not:o \l__xparse_process_one_tl } }
+    \tl_clear:N \l__xparse_process_one_tl
   }
-\cs_new_protected:cpn { __xparse_add_expandable_type_+:w }
+\cs_new_protected:Npn \__xparse_add_default:n #1
   {
-    \bool_set_true:N \l__xparse_long_bool
-    \int_compare:nNnTF \l__xparse_current_arg_int = \c_one
-      { \bool_set_true:N \l__xparse_all_long_bool }
+    \bool_set_true:N \l__xparse_defaults_bool
+    \tl_put_right:Nn \l__xparse_defaults_tl { { . #1} }
+  }
+\cs_new_protected:Npn \__xparse_add_default:
+  { \tl_put_right:Nn \l__xparse_defaults_tl { . } }
+\cs_new_protected:Npn \__xparse_add_default_E:nn #1#2
+  {
+    \bool_set_true:N \l__xparse_defaults_bool
+    \tl_set:Nx \l__xparse_tmpa_tl
       {
-        \bool_if:NF \l__xparse_all_long_bool
-          { \__msg_kernel_error:nn { xparse } { inconsistent-long } }
+        \exp_not:n {#2}
+        \prg_replicate:nn
+          { \tl_count:n {#1} - \tl_count:n {#2} }
+          { { \c__xparse_no_value_tl } }
+      }
+    \tl_put_right:Nx \l__xparse_defaults_tl
+      {
+        {
+          \exp_not:f
+            { \exp_after:wN \__xparse_add_default_E_aux:n \l__xparse_tmpa_tl }
+        }
       }
-    \int_decr:N \l__xparse_current_arg_int
-    \__xparse_prepare_signature:N
   }
-\cs_new_protected:cpn { __xparse_add_expandable_type_>:w } #1
+\cs_new:Npn \__xparse_add_default_E_aux:n #1 { {#1} }
+\cs_new_protected:cpn { __xparse_add_expandable_type_+:w }
   {
-    \__msg_kernel_error:nnx { xparse } { processor-in-expandable }
-      { \token_to_str:c { \l__xparse_function_tl } }
+    \bool_set_true:N \l__xparse_long_bool
     \int_decr:N \l__xparse_current_arg_int
     \__xparse_prepare_signature:N
   }
-\cs_new_protected:Npn \__xparse_add_expandable_type_d:w #1#2
-  {
-    \exp_args:NNNo
-      \__xparse_add_expandable_type_D:w #1 #2 \c__xparse_no_value_tl
-  }
-\cs_new_protected:Npn \__xparse_add_expandable_type_D:w #1#2
+\cs_new_protected:Npn \__xparse_add_expandable_type_D:w
+  { \__xparse_add_expandable_type_D_aux:NNNn D }
+\cs_new_protected:Npn \__xparse_add_expandable_type_D_aux:NNNn #1#2#3#4
   {
-    \tl_if_eq:nnTF {#1} {#2}
-      {
-        \__xparse_add_expandable_grabber_optional:n { D_alt }
-        \__xparse_add_expandable_type_D_aux:Nn #1
-      }
-      {
-        \__xparse_add_expandable_grabber_optional:n { D }
-        \__xparse_add_expandable_type_D_aux:NNn #1#2
-      }
+    \__xparse_add_default:n {#4}
+    \tl_if_eq:nnTF {#2} {#3}
+      { \__xparse_add_expandable_type_D_aux:NN #1 #2 }
+      { \__xparse_add_expandable_type_D_aux:NNN #1 #2 #3 }
+    \bool_set_false:N \l__xparse_long_bool
+    \__xparse_prepare_signature:N
   }
-\cs_new_protected:Npn \__xparse_add_expandable_type_D_aux:NNn #1#2#3
+\cs_new_protected:Npn \__xparse_add_expandable_type_D_aux:NNN #1#2#3
   {
+    \__xparse_add_expandable_grabber:n {#1}
     \bool_if:NTF \l__xparse_all_long_bool
       { \cs_set:cpx }
       { \cs_set_nopar:cpx }
-      { \l__xparse_expandable_aux_name_tl } ##1 ##2 #1 ##3 \q__xparse ##4 #2
+      { \l__xparse_expandable_aux_name_tl } ##1 ##2 #2 ##3 \q__xparse ##4 #3
       { ##1 {##2} {##3} {##4} }
     \tl_put_right:Nx \l__xparse_signature_tl
       {
         \exp_not:c  { \l__xparse_expandable_aux_name_tl }
-        \exp_not:n { #1 #2 {#3} }
+        \exp_not:n { #2 #3 }
       }
-    \bool_set_false:N \l__xparse_long_bool
-    \__xparse_prepare_signature:N
   }
-\cs_new_protected:Npn \__xparse_add_expandable_type_D_aux:Nn #1#2
+\cs_new_protected:Npn \__xparse_add_expandable_type_D_aux:NN #1#2
   {
+    \__xparse_add_expandable_grabber:n { #1_alt }
     \bool_if:NTF \l__xparse_all_long_bool
       { \cs_set:cpx }
       { \cs_set_nopar:cpx }
-      { \l__xparse_expandable_aux_name_tl } ##1 #1 ##2 #1
+      { \l__xparse_expandable_aux_name_tl } ##1 #2 ##2 #2
       { ##1 {##2} }
     \tl_put_right:Nx \l__xparse_signature_tl
       {
         \exp_not:c  { \l__xparse_expandable_aux_name_tl }
-        \exp_not:n { #1 {#2} }
+        \exp_not:n {#2}
       }
-    \bool_set_false:N \l__xparse_long_bool
-    \__xparse_prepare_signature:N
   }
-\cs_new_protected:Npn \__xparse_add_expandable_type_g:w
+\cs_new_protected:Npn \__xparse_add_expandable_type_E:w #1#2
   {
-    \__msg_kernel_error:nnx { xparse } { invalid-expandable-argument-type }
-      { g }
-    \__xparse_add_expandable_type_m:w
-  }
-\cs_new_protected:Npn \__xparse_add_expandable_type_G:w #1
-  {
-    \__msg_kernel_error:nnx { xparse } { invalid-expandable-argument-type }
-      { G }
-    \__xparse_add_expandable_type_m:w
-  }
-\cs_new_protected:Npn \__xparse_add_expandable_type_l:w
-  {
-    \__msg_kernel_error:nnx { xparse } { invalid-expandable-argument-type }
-      { l }
-    \__xparse_add_expandable_type_m:w
-  }
-\cs_new_protected:Npn \__xparse_add_expandable_type_m:w
-  {
-    \int_incr:N \l__xparse_m_args_int
-    \__xparse_add_expandable_grabber_mandatory:n { m }
+    \__xparse_add_default_E:nn {#1} {#2}
+    \__xparse_add_expandable_grabber:n { E }
+    \tl_clear:N \l__xparse_tmpb_tl
+    \tl_map_function:nN {#1} \__xparse_add_expandable_type_E_aux:n
+    \tl_put_right:Nx \l__xparse_signature_tl
+      {
+        { \exp_not:o \l__xparse_tmpb_tl }
+        {
+          \prg_replicate:nn { \tl_count:n {#1} }
+            { { \c__xparse_no_value_tl } }
+        }
+      }
     \bool_set_false:N \l__xparse_long_bool
     \__xparse_prepare_signature:N
   }
-\cs_new_protected:Npn \__xparse_add_expandable_type_r:w #1#2
+\cs_new_protected:Npn \__xparse_add_expandable_type_E_aux:n #1
   {
-    \exp_args:NNNo
-      \__xparse_add_expandable_type_R:w #1 #2 \c__xparse_no_value_tl
+    \__xparse_get_grabber:NN #1 \l__xparse_tmpa_tl
+    \tl_put_right:Nx \l__xparse_tmpb_tl
+      { \exp_not:o \l__xparse_tmpa_tl \exp_not:N #1 }
   }
-\cs_new_protected:Npn \__xparse_add_expandable_type_R:w #1#2
+\cs_new_protected:Npn \__xparse_add_expandable_type_m:w
   {
-    \tl_if_eq:nnTF {#1} {#2}
-      {
-        \__xparse_add_expandable_grabber_mandatory:n { R_alt }
-        \__xparse_add_expandable_type_D_aux:Nn #1
-      }
-      {
-        \__xparse_add_expandable_grabber_mandatory:n { R }
-        \__xparse_add_expandable_type_D_aux:NNn #1#2
-      }
+    \__xparse_add_default:
+    \__xparse_add_expandable_grabber:n { m }
+    \__xparse_prepare_signature:N
   }
+\cs_new_protected:Npn \__xparse_add_expandable_type_R:w
+  { \__xparse_add_expandable_type_D_aux:NNNn R }
 \cs_new_protected:Npn \__xparse_add_expandable_type_t:w #1
   {
-    \__xparse_add_expandable_grabber_optional:n { t }
-    \bool_if:NTF \l__xparse_all_long_bool
-      { \cs_set:cpn }
-      { \cs_set_nopar:cpn }
-      { \l__xparse_expandable_aux_name_tl } ##1 #1 {##1}
+    \__xparse_add_default:
+    \__xparse_add_expandable_grabber_t:
+    \__xparse_get_grabber:NN #1 \l__xparse_tmpa_tl
     \tl_put_right:Nx \l__xparse_signature_tl
       {
-        \exp_not:c { \l__xparse_expandable_aux_name_tl }
+        \exp_not:o \l__xparse_tmpa_tl
         \exp_not:N #1
       }
     \bool_set_false:N \l__xparse_long_bool
     \__xparse_prepare_signature:N
   }
-\cs_new_protected:Npn \__xparse_add_expandable_type_u:w #1
-  {
-    \__msg_kernel_error:nnx { xparse } { invalid-expandable-argument-type }
-      { u }
-    \__xparse_add_expandable_type_m:w
-  }
-\cs_new_protected:Npn \__xparse_add_expandable_type_v:w
+\cs_new_protected:Npn \__xparse_add_expandable_grabber:n #1
   {
-    \__msg_kernel_error:nnx { xparse } { invalid-expandable-argument-type }
-      { v }
-    \__xparse_add_expandable_type_m:w
-  }
-\cs_new_protected:Npn \__xparse_add_expandable_grabber_mandatory:n #1
-  {
-    \__xparse_add_expandable_long_check:
+    \bool_if:NTF \l__xparse_all_long_set_bool
+      {
+        \bool_if:nT
+          { \bool_xor_p:nn { \l__xparse_all_long_bool } { \l__xparse_long_bool } }
+          {
+            \__msg_kernel_error:nnx { xparse } { inconsistent-long }
+              { \iow_char:N \\ \l__xparse_function_tl }
+            \__xparse_bad_def:wn
+          }
+      }
+      {
+        \bool_set:Nn \l__xparse_all_long_bool { \l__xparse_long_bool }
+        \bool_set_true:N \l__xparse_all_long_set_bool
+      }
     \tl_put_right:Nx \l__xparse_signature_tl
       { \exp_not:c { __xparse_expandable_grab_ #1 :w } }
     \bool_set_false:N \l__xparse_long_bool
-    \int_decr:N \l__xparse_mandatory_args_int
   }
-\cs_new_protected:Npn \__xparse_add_expandable_grabber_optional:n #1
+\cs_new_protected:Npn \__xparse_add_expandable_grabber_t:
   {
-    \__xparse_add_expandable_long_check:
-    \int_compare:nNnF \l__xparse_mandatory_args_int > \c_zero
-      { \__msg_kernel_error:nn { xparse } { expandable-ending-optional } }
-    \tl_put_right:Nx \l__xparse_signature_tl
-      { \exp_not:c { __xparse_expandable_grab_ #1 :w } }
+    \tl_put_right:Nn \l__xparse_signature_tl
+      { \__xparse_expandable_grab_t:w }
     \bool_set_false:N \l__xparse_long_bool
   }
-\cs_new_protected:Npn \__xparse_add_expandable_long_check:
+\cs_new_protected:Npn \__xparse_get_grabber:NN #1#2
   {
-    \bool_if:nT { \l__xparse_all_long_bool && ! \l__xparse_long_bool }
-      { \__msg_kernel_error:nn { xparse } { inconsistent-long } }
+    \cs_set:Npn \__xparse_tmp:w ##1 #1 {##1}
+    \exp_args:Nc \__xparse_get_grabber_auxi:NN
+      { __xparse_grabber_ \token_to_str:N #1 :w } #2
   }
-\cs_new_protected:Npn \__xparse_grab_arg:w { }
-\cs_new_protected:Npn \__xparse_grab_arg_auxi:w { }
-\cs_new_protected:Npn \__xparse_grab_arg_auxii:w { }
-\cs_new_protected:Npn \__xparse_grab_D:w #1#2#3#4 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_get_grabber_auxi:NN #1#2
   {
-    \__xparse_grab_D_aux:NNnnNn #1 #2 {#3} {#4} \cs_set_protected_nopar:Npn
+    \cs_if_eq:NNTF \__xparse_tmp:w #1
+      { \tl_set:Nn #2 {#1} }
+      {
+        \cs_if_exist:NTF #1
+          {
+            \int_gincr:N \g__xparse_grabber_int
+            \exp_args:Nc \__xparse_get_grabber_auxi:NN
+              {
+                __xparse_grabber_
+                - \int_use:N \g__xparse_grabber_int :w
+              }
+              #2
+          }
+          { \__xparse_get_grabber_auxii:NN #1 #2 }
+      }
+  }
+\cs_new_protected:Npn \__xparse_get_grabber_auxii:NN #1#2
+  {
+    \cs_set_eq:NN #1 \__xparse_tmp:w
+    \tl_set:Nn #2 {#1}
+  }
+\cs_new_protected:Npn \__xparse_grab_D:w #1#2#3 \__xparse_run_code:
+  {
+    \__xparse_grab_D_aux:NNnNn #1 #2 {#3} \cs_set_protected_nopar:Npn
       { _ignore_spaces }
   }
-\cs_new_protected:Npn \__xparse_grab_D_long:w #1#2#3#4 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_D_long:w #1#2#3 \__xparse_run_code:
   {
-    \__xparse_grab_D_aux:NNnnNn #1 #2 {#3} {#4} \cs_set_protected:Npn
+    \__xparse_grab_D_aux:NNnNn #1 #2 {#3} \cs_set_protected:Npn
       { _ignore_spaces }
   }
-\cs_new_protected:Npn \__xparse_grab_D_trailing:w #1#2#3#4 \l__xparse_args_tl
-  { \__xparse_grab_D_aux:NNnnNn #1 #2 {#3} {#4} \cs_set_protected_nopar:Npn { } }
-\cs_new_protected:Npn \__xparse_grab_D_long_trailing:w #1#2#3#4 \l__xparse_args_tl
-  { \__xparse_grab_D_aux:NNnnNn #1 #2 {#3} {#4} \cs_set_protected:Npn { } }
-\cs_new_protected:Npn \__xparse_grab_D_aux:NNnnNn #1#2#3#4#5#6
+\cs_new_protected:Npn \__xparse_grab_D_trailing:w #1#2#3 \__xparse_run_code:
+  { \__xparse_grab_D_aux:NNnNn #1 #2 {#3} \cs_set_protected_nopar:Npn { } }
+\cs_new_protected:Npn \__xparse_grab_D_long_trailing:w #1#2#3 \__xparse_run_code:
+  { \__xparse_grab_D_aux:NNnNn #1 #2 {#3} \cs_set_protected:Npn { } }
+\cs_new_protected:Npn \__xparse_grab_D_aux:NNnNn #1#2#3#4#5
   {
-    \__xparse_grab_D_aux:NNnN #1#2 {#4} #5
-    \use:c { peek_meaning_remove #6 :NTF } #1
-      { \__xparse_grab_arg:w }
-      {
-        \__xparse_add_arg:n {#3}
-        #4 \l__xparse_args_tl
-      }
+    \__xparse_grab_D_aux:NNnN #1#2 {#3} #4
+    \use:c { peek_meaning_remove #5 :NTF } #1
+      { \__xparse_grab_D_call:Nw #1 }
+      { \__xparse_add_arg:o \c__xparse_no_value_tl }
   }
 \cs_new_protected:Npn \__xparse_grab_D_aux:NNnN #1#2#3#4
   {
-    \cs_set_protected_nopar:Npn \__xparse_grab_arg:w
+    \tl_set:Nn \l__xparse_signature_tl {#3}
+    \exp_after:wN #4 \l__xparse_fn_tl ##1 #2
       {
-        \exp_after:wN #4 \l__xparse_fn_tl ####1 #2
+        \tl_if_in:nnTF {##1} {#1}
+          { \__xparse_grab_D_nested:NNnN #1 #2 {##1} #4 }
           {
-            \tl_if_in:nnTF {####1} {#1}
-              { \__xparse_grab_D_nested:NNnnN #1 #2 {####1} {#3} #4 }
+            \tl_if_blank:oTF { \use_none:n ##1 }
+              { \__xparse_add_arg:o { \use_none:n ##1 } }
               {
-                \tl_if_blank:oTF { \use_none:n ####1 }
-                  { \__xparse_add_arg:o { \use_none:n ####1 } }
-                  {
-                    \str_if_eq_x:nnTF
-                      { \exp_not:o { \use_none:n ####1 } }
-                      { { \exp_not:o { \use_ii:nnn ####1 \q_nil } } }
-                      { \__xparse_add_arg:o { \use_ii:nn ####1 } }
-                      { \__xparse_add_arg:o { \use_none:n ####1 } }
-                  }
-                #3 \l__xparse_args_tl
+                \str_if_eq_x:nnTF
+                  { \exp_not:o { \use_none:n ##1 } }
+                  { { \exp_not:o { \use_ii:nnn ##1 \q_nil } } }
+                  { \__xparse_add_arg:o { \use_ii:nn ##1 } }
+                  { \__xparse_add_arg:o { \use_none:n ##1 } }
               }
           }
-        \token_if_eq_catcode:NNTF + #1
-          {
-            \exp_after:wN \exp_after:wN \exp_after:wN
-              \l__xparse_fn_tl \char_generate:nn { `#1 } { 11 }
-          }
-          {
-            \exp_after:wN \l__xparse_fn_tl
-            \token_to_str:N #1
-          }
       }
   }
 \tl_new:N \l__xparse_nesting_a_tl
 \tl_new:N \l__xparse_nesting_b_tl
 \quark_new:N \q__xparse
-\cs_new_protected:Npn \__xparse_grab_D_nested:NNnnN #1#2#3#4#5
+\cs_new_protected:Npn \__xparse_grab_D_nested:NNnN #1#2#3#4
   {
     \tl_clear:N \l__xparse_nesting_a_tl
     \tl_clear:N \l__xparse_nesting_b_tl
-    \exp_after:wN #5 \l__xparse_fn_tl ##1 #1 ##2 \q__xparse ##3 #2
+    \exp_after:wN #4 \l__xparse_fn_tl ##1 #1 ##2 \q__xparse ##3 #2
       {
         \tl_put_right:No \l__xparse_nesting_a_tl { \use_none:n ##1 #1 }
         \tl_put_right:No \l__xparse_nesting_b_tl { \use_i:nn #2 ##3 }
@@ -714,7 +967,6 @@
                 \tl_put_right:No \l__xparse_nesting_a_tl
                   \l__xparse_nesting_b_tl
                 \__xparse_add_arg:V \l__xparse_nesting_a_tl
-                #4 \l__xparse_args_tl
               }
           }
       }
@@ -722,44 +974,51 @@
   }
 \cs_new:Npn \__xparse_grab_D_nested:w #1 \q_nil \q_stop
   { \exp_not:o { \use_none:n #1 } }
-\cs_new_protected:Npn \__xparse_grab_E:w #1#2#3 \l__xparse_args_tl
+\cs_set_protected_nopar:Npn \__xparse_grab_D_call:Nw #1
   {
-    \__xparse_grab_E:nnnNn
-       {#1} {#2} {#3}
+    \token_if_eq_catcode:NNTF + #1
+      {
+        \exp_after:wN \exp_after:wN \exp_after:wN
+          \l__xparse_fn_tl \char_generate:nn { `#1 } { 11 }
+      }
+      {
+        \exp_after:wN \l__xparse_fn_tl
+        \token_to_str:N #1
+      }
+  }
+\cs_new_protected:Npn \__xparse_grab_E:w #1#2 \__xparse_run_code:
+  {
+    \__xparse_grab_E:nnNn {#1} {#2}
       \cs_set_protected_nopar:Npn
       { _ignore_spaces }
   }
-\cs_new_protected:Npn \__xparse_grab_E_long:w #1#2#3 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_E_long:w #1#2 \__xparse_run_code:
   {
-    \__xparse_grab_E:nnnNn
-       {#1} {#2} {#3}
+    \__xparse_grab_E:nnNn {#1} {#2}
       \cs_set_protected:Npn
       { _ignore_spaces }
   }
-\cs_new_protected:Npn \__xparse_grab_E_trailing:w #1#2#3 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_E_trailing:w #1#2 \__xparse_run_code:
   {
-    \__xparse_grab_E:nnnNn
-       {#1} {#2} {#3}
+    \__xparse_grab_E:nnNn {#1} {#2}
       \cs_set_protected_nopar:Npn
       { }
   }
-\cs_new_protected:Npn \__xparse_grab_E_long_trailing:w #1#2#3 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_E_long_trailing:w #1#2 \__xparse_run_code:
   {
-    \__xparse_grab_E:nnnNn
-       {#1} {#2} {#3}
+    \__xparse_grab_E:nnNn {#1} {#2}
       \cs_set_protected:Npn
       { }
   }
-\cs_new_protected:Npn \__xparse_grab_E:nnnNn #1#2#3#4#5
+\cs_new_protected:Npn \__xparse_grab_E:nnNn #1#2#3#4
   {
-    \exp_after:wN #4 \l__xparse_fn_tl ##1##2##3
+    \exp_after:wN #3 \l__xparse_fn_tl ##1##2##3
       {
         \prop_put:Nnn \l__xparse_tmp_prop {##1} {##3}
-        \__xparse_grab_E_loop:nnN {#5} { } ##2 \q_recursion_stop
+        \__xparse_grab_E_loop:nnN {#4} { } ##2 \q_recursion_stop
       }
     \prop_clear:N \l__xparse_tmp_prop
-    \__xparse_grab_E_setup:Nw
-      #1 \q_recursion_tail \q_mark #2 \q_recursion_tail \q_recursion_stop
+    \tl_set:Nn \l__xparse_signature_tl {#2}
     \cs_set_protected:Npn \__xparse_grab_E_finalise:
       {
         \tl_clear:N \l__xparse_tmpa_tl
@@ -774,16 +1033,8 @@
               }
           }
         \__xparse_add_arg:V \l__xparse_tmpa_tl
-        #3 \l__xparse_args_tl
       }
-    \__xparse_grab_E_loop:nnN {#5} { } #1 \q_recursion_tail \q_recursion_stop
-  }
-\cs_new_protected:Npn \__xparse_grab_E_setup:Nw #1#2 \q_mark #3
-  {
-    \quark_if_recursion_tail_stop:N #1
-    \quark_if_recursion_tail_stop:n {#3}
-    \prop_put:Nnn \l__xparse_tmp_prop {#1} {#3}
-    \__xparse_grab_E_setup:Nw #2 \q_mark
+    \__xparse_grab_E_loop:nnN {#4} { } #1 \q_recursion_tail \q_recursion_stop
   }
 \cs_new_protected:Npn \__xparse_grab_E_loop:nnN #1#2#3#4 \q_recursion_stop
   {
@@ -796,203 +1047,156 @@
       }
   }
 \cs_new_protected:Npn \__xparse_grab_E_finalise: { }
-\cs_new_protected:Npn \__xparse_grab_G:w #1#2 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_G:w #1 \__xparse_run_code:
   {
-    \__xparse_grab_G_aux:nnNn {#1} {#2} \cs_set_protected_nopar:Npn
+    \__xparse_grab_G_aux:nNn {#1} \cs_set_protected_nopar:Npn
       { _ignore_spaces }
   }
-\cs_new_protected:Npn \__xparse_grab_G_long:w #1#2 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_G_long:w #1 \__xparse_run_code:
   {
-    \__xparse_grab_G_aux:nnNn {#1} {#2} \cs_set_protected:Npn { _ignore_spaces }
+    \__xparse_grab_G_aux:nNn {#1} \cs_set_protected:Npn { _ignore_spaces }
   }
-\cs_new_protected:Npn \__xparse_grab_G_trailing:w #1#2 \l__xparse_args_tl
-  { \__xparse_grab_G_aux:nnNn {#1} {#2} \cs_set_protected_nopar:Npn { } }
-\cs_new_protected:Npn \__xparse_grab_G_long_trailing:w #1#2 \l__xparse_args_tl
-  { \__xparse_grab_G_aux:nnNn {#1} {#2} \cs_set_protected:Npn { } }
-\cs_new_protected:Npn \__xparse_grab_G_aux:nnNn #1#2#3#4
+\cs_new_protected:Npn \__xparse_grab_G_trailing:w #1 \__xparse_run_code:
+  { \__xparse_grab_G_aux:nNn {#1} \cs_set_protected_nopar:Npn { } }
+\cs_new_protected:Npn \__xparse_grab_G_long_trailing:w #1 \__xparse_run_code:
+  { \__xparse_grab_G_aux:nNn {#1} \cs_set_protected:Npn { } }
+\cs_new_protected:Npn \__xparse_grab_G_aux:nNn #1#2#3
   {
-    \exp_after:wN #3 \l__xparse_fn_tl ##1
-      {
-        \__xparse_add_arg:n {##1}
-        #2 \l__xparse_args_tl
-      }
-    \use:c { peek_meaning #4 :NTF } \c_group_begin_token
+    \tl_set:Nn \l__xparse_signature_tl {#1}
+    \exp_after:wN #2 \l__xparse_fn_tl ##1
+      { \__xparse_add_arg:n {##1} }
+    \use:c { peek_meaning #3 :NTF } \c_group_begin_token
       { \l__xparse_fn_tl }
-      {
-        \__xparse_add_arg:n {#1}
-        #2 \l__xparse_args_tl
-      }
+      { \__xparse_add_arg:o \c__xparse_no_value_tl }
   }
-\cs_new_protected:Npn \__xparse_grab_l:w #1 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_l:w #1 \__xparse_run_code:
   { \__xparse_grab_l_aux:nN {#1} \cs_set_protected_nopar:Npn }
-\cs_new_protected:Npn \__xparse_grab_l_long:w #1 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_l_long:w #1 \__xparse_run_code:
   { \__xparse_grab_l_aux:nN {#1} \cs_set_protected:Npn }
 \cs_new_protected:Npn \__xparse_grab_l_aux:nN #1#2
   {
+    \tl_set:Nn \l__xparse_signature_tl {#1}
     \exp_after:wN #2 \l__xparse_fn_tl ##1##
-      {
-        \__xparse_add_arg:n {##1}
-        #1 \l__xparse_args_tl
-      }
+      { \__xparse_add_arg:n {##1} }
     \l__xparse_fn_tl
   }
-\cs_new_protected:Npn \__xparse_grab_m:w #1 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_m:w #1 \__xparse_run_code:
   {
+    \tl_set:Nn \l__xparse_signature_tl {#1}
     \exp_after:wN \cs_set_protected_nopar:Npn \l__xparse_fn_tl ##1
-      {
-        \__xparse_add_arg:n {##1}
-        #1 \l__xparse_args_tl
-      }
+      { \__xparse_add_arg:n {##1} }
     \l__xparse_fn_tl
   }
-\cs_new_protected:Npn \__xparse_grab_m_long:w #1 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_m_long:w #1 \__xparse_run_code:
   {
+    \tl_set:Nn \l__xparse_signature_tl {#1}
     \exp_after:wN \cs_set_protected:Npn \l__xparse_fn_tl ##1
-      {
-        \__xparse_add_arg:n {##1}
-        #1 \l__xparse_args_tl
-      }
+      { \__xparse_add_arg:n {##1} }
     \l__xparse_fn_tl
   }
-\cs_new_protected:cpn { __xparse_grab_m_1:w } #1 \l__xparse_args_tl
+\cs_new_protected_nopar:Npn \__xparse_grab_m_aux:Nnnnnnnnn #1#2#3#4#5#6#7#8#9
   {
-    \exp_after:wN \cs_set_protected_nopar:Npn \l__xparse_fn_tl ##1
-      {
-        \tl_put_right:Nn \l__xparse_args_tl { {##1} }
-        #1 \l__xparse_args_tl
-      }
-    \l__xparse_fn_tl
+    \tl_put_right:No \l__xparse_args_tl
+      { #1 {#2} {#3} {#4} {#5} {#6} {#7} {#8} {#9} }
+    \l__xparse_signature_tl \__xparse_run_code:
   }
-\cs_new_protected:cpn { __xparse_grab_m_2:w } #1 \l__xparse_args_tl
+\cs_new_protected:cpn { __xparse_grab_m_1:w } #1 \__xparse_run_code:
   {
-    \exp_after:wN \cs_set_protected_nopar:Npn \l__xparse_fn_tl
-      ##1##2
-      {
-        \tl_put_right:Nn \l__xparse_args_tl { {##1} {##2} }
-        #1 \l__xparse_args_tl
-      }
-    \l__xparse_fn_tl
+    \tl_set:Nn \l__xparse_signature_tl {#1}
+    \exp_after:wN \cs_set_eq:NN \l__xparse_fn_tl \__xparse_grab_m_aux:Nnnnnnnnn
+    \l__xparse_fn_tl \use_none:nnnnnnn { } { } { } { } { } { } { }
   }
-\cs_new_protected:cpn { __xparse_grab_m_3:w } #1 \l__xparse_args_tl
+\cs_new_protected:cpn { __xparse_grab_m_2:w } #1 \__xparse_run_code:
   {
-    \exp_after:wN \cs_set_protected_nopar:Npn \l__xparse_fn_tl
-      ##1##2##3
-      {
-        \tl_put_right:Nn \l__xparse_args_tl { {##1} {##2} {##3} }
-        #1 \l__xparse_args_tl
-      }
-    \l__xparse_fn_tl
+    \tl_set:Nn \l__xparse_signature_tl {#1}
+    \exp_after:wN \cs_set_eq:NN \l__xparse_fn_tl \__xparse_grab_m_aux:Nnnnnnnnn
+    \l__xparse_fn_tl \use_none:nnnnnn { } { } { } { } { } { }
   }
-\cs_new_protected:cpn { __xparse_grab_m_4:w } #1 \l__xparse_args_tl
+\cs_new_protected:cpn { __xparse_grab_m_3:w } #1 \__xparse_run_code:
   {
-    \exp_after:wN \cs_set_protected_nopar:Npn \l__xparse_fn_tl
-      ##1##2##3##4
-      {
-        \tl_put_right:Nn \l__xparse_args_tl { {##1} {##2} {##3} {##4} }
-        #1 \l__xparse_args_tl
-      }
-    \l__xparse_fn_tl
+    \tl_set:Nn \l__xparse_signature_tl {#1}
+    \exp_after:wN \cs_set_eq:NN \l__xparse_fn_tl \__xparse_grab_m_aux:Nnnnnnnnn
+    \l__xparse_fn_tl \use_none:nnnnn { } { } { } { } { }
   }
-\cs_new_protected:cpn { __xparse_grab_m_5:w } #1 \l__xparse_args_tl
+\cs_new_protected:cpn { __xparse_grab_m_4:w } #1 \__xparse_run_code:
   {
-    \exp_after:wN \cs_set_protected_nopar:Npn \l__xparse_fn_tl
-      ##1##2##3##4##5
-      {
-        \tl_put_right:Nn \l__xparse_args_tl { {##1} {##2} {##3} {##4} {##5} }
-        #1 \l__xparse_args_tl
-      }
-    \l__xparse_fn_tl
+    \tl_set:Nn \l__xparse_signature_tl {#1}
+    \exp_after:wN \cs_set_eq:NN \l__xparse_fn_tl \__xparse_grab_m_aux:Nnnnnnnnn
+    \l__xparse_fn_tl \use_none:nnnn { } { } { } { }
   }
-\cs_new_protected:cpn { __xparse_grab_m_6:w } #1 \l__xparse_args_tl
+\cs_new_protected:cpn { __xparse_grab_m_5:w } #1 \__xparse_run_code:
   {
-    \exp_after:wN \cs_set_protected_nopar:Npn \l__xparse_fn_tl
-      ##1##2##3##4##5##6
-      {
-        \tl_put_right:Nn \l__xparse_args_tl
-          { {##1} {##2} {##3} {##4} {##5} {##6} }
-        #1 \l__xparse_args_tl
-      }
-    \l__xparse_fn_tl
+    \tl_set:Nn \l__xparse_signature_tl {#1}
+    \exp_after:wN \cs_set_eq:NN \l__xparse_fn_tl \__xparse_grab_m_aux:Nnnnnnnnn
+    \l__xparse_fn_tl \use_none:nnn { } { } { }
   }
-\cs_new_protected:cpn { __xparse_grab_m_7:w } #1 \l__xparse_args_tl
+\cs_new_protected:cpn { __xparse_grab_m_6:w } #1 \__xparse_run_code:
   {
-    \exp_after:wN \cs_set_protected_nopar:Npn \l__xparse_fn_tl
-      ##1##2##3##4##5##6##7
-      {
-        \tl_put_right:Nn \l__xparse_args_tl
-          { {##1} {##2} {##3} {##4} {##5} {##6} {##7} }
-        #1 \l__xparse_args_tl
-      }
-    \l__xparse_fn_tl
+    \tl_set:Nn \l__xparse_signature_tl {#1}
+    \exp_after:wN \cs_set_eq:NN \l__xparse_fn_tl \__xparse_grab_m_aux:Nnnnnnnnn
+    \l__xparse_fn_tl \use_none:nn { } { }
   }
-\cs_new_protected:cpn { __xparse_grab_m_8:w } #1 \l__xparse_args_tl
+\cs_new_protected:cpn { __xparse_grab_m_7:w } #1 \__xparse_run_code:
   {
-    \exp_after:wN \cs_set_protected_nopar:Npn \l__xparse_fn_tl
-      ##1##2##3##4##5##6##7##8
-      {
-        \tl_put_right:Nn \l__xparse_args_tl
-          { {##1} {##2} {##3} {##4} {##5} {##6} {##7} {##8} }
-        #1 \l__xparse_args_tl
-      }
-    \l__xparse_fn_tl
+    \tl_set:Nn \l__xparse_signature_tl {#1}
+    \exp_after:wN \cs_set_eq:NN \l__xparse_fn_tl \__xparse_grab_m_aux:Nnnnnnnnn
+    \l__xparse_fn_tl \use_none:n { }
   }
-\cs_new_protected:Npn \__xparse_grab_R:w #1#2#3#4 \l__xparse_args_tl
-  { \__xparse_grab_R_aux:NNnnN #1 #2 {#3} {#4} \cs_set_protected_nopar:Npn }
-\cs_new_protected:Npn \__xparse_grab_R_long:w #1#2#3#4 \l__xparse_args_tl
-  { \__xparse_grab_R_aux:NNnnN #1 #2 {#3} {#4} \cs_set_protected:Npn }
-\cs_new_protected:Npn \__xparse_grab_R_aux:NNnnN #1#2#3#4#5
+\cs_new_protected:cpn { __xparse_grab_m_8:w } #1 \__xparse_run_code:
   {
-    \__xparse_grab_D_aux:NNnN #1 #2 {#4} #5
+    \tl_set:Nn \l__xparse_signature_tl {#1}
+    \exp_after:wN \cs_set_eq:NN \l__xparse_fn_tl \__xparse_grab_m_aux:Nnnnnnnnn
+    \l__xparse_fn_tl \prg_do_nothing:
+  }
+\cs_new_protected:cpx { __xparse_grab_m_9:w }
+  {
+    \exp_not:c { __xparse_grab_m_5:w }
+    \exp_not:c { __xparse_grab_m_4:w }
+  }
+\cs_new_protected:Npn \__xparse_grab_R:w #1#2#3 \__xparse_run_code:
+  { \__xparse_grab_R_aux:NNnN #1 #2 {#3} \cs_set_protected_nopar:Npn }
+\cs_new_protected:Npn \__xparse_grab_R_long:w #1#2#3 \__xparse_run_code:
+  { \__xparse_grab_R_aux:NNnN #1 #2 {#3} \cs_set_protected:Npn }
+\cs_new_protected:Npn \__xparse_grab_R_aux:NNnN #1#2#3#4
+  {
+    \__xparse_grab_D_aux:NNnN #1 #2 {#3} #4
     \peek_meaning_remove_ignore_spaces:NTF #1
-      { \__xparse_grab_arg:w }
+      { \__xparse_grab_D_call:Nw #1 }
       {
         \__msg_kernel_error:nnxx { xparse } { missing-required }
-          { \token_to_str:N #1 } { \tl_to_str:n {#3} }
-        \__xparse_add_arg:n {#3}
-        #4 \l__xparse_args_tl
+          { \exp_after:wN \token_to_str:N \l__xparse_fn_tl }
+          { \token_to_str:N #1 }
+        \__xparse_add_arg:o \c__xparse_no_value_tl
       }
   }
-\cs_new_protected:Npn \__xparse_grab_t:w #1#2 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_t:w
+  { \__xparse_grab_t_aux:NNw \peek_meaning_remove_ignore_spaces:NTF }
+\cs_new_eq:NN \__xparse_grab_t_long:w \__xparse_grab_t:w
+\cs_new_protected:Npn \__xparse_grab_t_trailing:w
+  { \__xparse_grab_t_aux:NNw \peek_meaning_remove:NTF }
+\cs_new_eq:NN \__xparse_grab_t_long_trailing:w \__xparse_grab_t_trailing:w
+\cs_new_protected:Npn \__xparse_grab_t_aux:NNw #1#2#3 \__xparse_run_code:
   {
-    \__xparse_grab_t_aux:NnNn #1 {#2} \cs_set_protected_nopar:Npn
-      { _ignore_spaces }
-  }
-\cs_new_protected:Npn \__xparse_grab_t_long:w #1#2 \l__xparse_args_tl
-  { \__xparse_grab_t_aux:NnNn #1 {#2} \cs_set_protected:Npn { _ignore_spaces } }
-\cs_new_protected:Npn \__xparse_grab_t_trailing:w #1#2 \l__xparse_args_tl
-  { \__xparse_grab_t_aux:NnNn #1 {#2} \cs_set_protected_nopar:Npn { } }
-\cs_new_protected:Npn \__xparse_grab_t_long_trailing:w #1#2 \l__xparse_args_tl
-  { \__xparse_grab_t_aux:NnNn #1 {#2} \cs_set_protected:Npn { } }
-\cs_new_protected:Npn \__xparse_grab_t_aux:NnNn #1#2#3#4
-  {
-    \exp_after:wN #3 \l__xparse_fn_tl
+    \tl_set:Nn \l__xparse_signature_tl {#3}
+    \exp_after:wN \cs_set_protected:Npn \l__xparse_fn_tl
       {
-        \use:c { peek_meaning_remove #4 :NTF } #1
-          {
-            \__xparse_add_arg:n { \BooleanTrue }
-            #2 \l__xparse_args_tl
-          }
-          {
-            \__xparse_add_arg:n { \BooleanFalse }
-            #2 \l__xparse_args_tl
-          }
+        #1 #2
+          { \__xparse_add_arg:n { \BooleanTrue } }
+          { \__xparse_add_arg:n { \BooleanFalse } }
       }
     \l__xparse_fn_tl
   }
-\cs_new_protected:Npn \__xparse_grab_u:w #1#2 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_u:w #1#2 \__xparse_run_code:
   { \__xparse_grab_u_aux:nnN {#1} {#2} \cs_set_protected_nopar:Npn }
-\cs_new_protected:Npn \__xparse_grab_u_long:w #1#2 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_u_long:w #1#2 \__xparse_run_code:
   { \__xparse_grab_u_aux:nnN {#1} {#2} \cs_set_protected:Npn }
 \cs_new_protected:Npn \__xparse_grab_u_aux:nnN #1#2#3
   {
+    \tl_set:Nn \l__xparse_signature_tl {#2}
     \exp_after:wN #3 \l__xparse_fn_tl ##1 #1
-      {
-        \__xparse_add_arg:n {##1}
-        #2 \l__xparse_args_tl
-      }
+      { \__xparse_add_arg:n {##1} }
     \l__xparse_fn_tl
   }
-\tl_new:N \l__xparse_v_rest_of_signature_tl
 \tl_new:N \l__xparse_v_arg_tl
 \cs_new_protected:Npn \__xparse_grab_v:w
   {
@@ -1004,9 +1208,9 @@
     \bool_set_true:N \l__xparse_long_bool
     \__xparse_grab_v_aux:w
   }
-\cs_new_protected:Npn \__xparse_grab_v_aux:w #1 \l__xparse_args_tl
+\cs_new_protected:Npn \__xparse_grab_v_aux:w #1 \__xparse_run_code:
   {
-    \tl_set:Nn \l__xparse_v_rest_of_signature_tl {#1}
+    \tl_set:Nn \l__xparse_signature_tl {#1}
     \group_begin:
       \group_align_safe_begin:
         \tex_escapechar:D = 92 \scan_stop:
@@ -1061,8 +1265,7 @@
 \cs_new_protected:Npn \__xparse_grab_v_aux_loop_end:
   {
     \__xparse_grab_v_group_end:
-    \exp_args:Nx \__xparse_add_arg:n { \tl_tail:N \l__xparse_v_arg_tl }
-    \l__xparse_v_rest_of_signature_tl \l__xparse_args_tl
+    \__xparse_add_arg:x { \tl_tail:N \l__xparse_v_arg_tl }
   }
 \int_new:N \l__xparse_v_nesting_int
 \cs_new_protected:Npx \__xparse_grab_v_bgroup:
@@ -1113,7 +1316,6 @@
 \cs_new_protected:Npn \__xparse_grab_v_aux_abort:n #1
   {
     \__xparse_grab_v_group_end:
-    \__xparse_add_arg:o \c__xparse_no_value_tl
     \exp_after:wN \exp_after:wN \exp_after:wN
       \peek_meaning_remove:NTF \char_generate:nn { \tex_endlinechar:D } { 6 }
       {
@@ -1121,14 +1323,14 @@
           { \exp_after:wN \token_to_str:N \l__xparse_fn_tl }
           { \tl_to_str:N \l__xparse_v_arg_tl }
           { \tl_to_str:n {#1} }
-        \l__xparse_v_rest_of_signature_tl \l__xparse_args_tl
+        \__xparse_add_arg:o \c__xparse_no_value_tl
       }
       {
         \__msg_kernel_error:nnxxx { xparse } { verbatim-tokenized }
           { \exp_after:wN \token_to_str:N \l__xparse_fn_tl }
           { \tl_to_str:N \l__xparse_v_arg_tl }
           { \tl_to_str:n {#1} }
-        \l__xparse_v_rest_of_signature_tl \l__xparse_args_tl
+        \__xparse_add_arg:o \c__xparse_no_value_tl
       }
   }
 \cs_new_protected:Npn \__xparse_grab_v_aux_put:N #1
@@ -1143,45 +1345,28 @@
   { \str_if_eq_x:nnTF { } { \str_tail:n {#1} } }
 \cs_new_protected:Npn \__xparse_add_arg:n #1
   {
-    \int_compare:nNnTF \l__xparse_processor_int = \c_zero
-      { \tl_put_right:Nn \l__xparse_args_tl { {#1} } }
-      {
-        \tl_clear:N \ProcessedArgument
-        \__xparse_if_no_value:nTF {#1}
-          {
-            \int_zero:N \l__xparse_processor_int
-            \tl_put_right:Nn \l__xparse_args_tl { {#1} }
-          }
-          { \__xparse_add_arg_aux:n {#1} }
-      }
+    \tl_put_right:Nn \l__xparse_args_tl { {#1} }
+    \l__xparse_signature_tl \__xparse_run_code:
   }
-\cs_generate_variant:Nn \__xparse_add_arg:n { V , o }
-\cs_new_protected:Npn \__xparse_add_arg_aux:n #1
-  {
-    \use:c { __xparse_processor_ \int_use:N \l__xparse_processor_int :n } {#1}
-    \int_decr:N \l__xparse_processor_int
-    \int_compare:nNnTF \l__xparse_processor_int = \c_zero
-      {
-        \tl_put_right:Nx \l__xparse_args_tl
-          { { \exp_not:V \ProcessedArgument } }
-      }
-      { \__xparse_add_arg_aux:V \ProcessedArgument }
-}
-\cs_generate_variant:Nn \__xparse_add_arg_aux:n { V }
+\cs_generate_variant:Nn \__xparse_add_arg:n { V , o , x }
 \cs_new:Npn \__xparse_expandable_grab_D:w #1 \q__xparse #2
-  { #2 { \__xparse_expandable_grab_D:NNNnwNn #1 \q__xparse #2 } }
-\cs_new:Npn \__xparse_expandable_grab_D:NNNnwNn #1#2#3#4#5 \q__xparse #6#7
+  { #2 { \__xparse_expandable_grab_D:NNNwNn #1 \q__xparse #2 } }
+\cs_set_protected:Npn \__xparse_tmp:w #1
   {
-    \str_if_eq:onTF
-      { #1 { } { } #7 #2 \q__xparse #3 }
-      { { } {#2} { } }
+    \cs_new:Npn \__xparse_expandable_grab_D:NNNwNn ##1##2##3##4 \q__xparse ##5##6
       {
-        #1
-          { \__xparse_expandable_grab_D:NNNwNnnn #1#2#3#5 \q__xparse #6 }
-          \q_nil { } #2 \ERROR \q__xparse \ERROR
+        \str_if_eq:onTF
+          { ##1 { } { } ##6 ##2 \q__xparse ##3 }
+          { { } {##2} { } }
+          {
+            ##1
+              { \__xparse_expandable_grab_D:NNNwNnnn ##1##2##3##4 \q__xparse ##5 }
+              \q_nil { } ##2 \ERROR \q__xparse \ERROR
+          }
+          { ##4 {#1} \q__xparse ##5 {##6} }
       }
-      { #5 {#4} \q__xparse #6 {#7} }
   }
+\exp_args:No \__xparse_tmp:w { \c__xparse_no_value_tl }
 \cs_new:Npn \__xparse_expandable_grab_D:NNNwNnnn #1#2#3#4 \q__xparse #5#6#7#8
   {
     \exp_args:Nof \__xparse_expandable_grab_D:nnNNNwN
@@ -1213,19 +1398,23 @@
       }
   }
 \cs_new:Npn \__xparse_expandable_grab_D_alt:w #1 \q__xparse #2
-  { #2 { \__xparse_expandable_grab_D_alt:NNnwNn #1 \q__xparse #2 } }
-\cs_new:Npn \__xparse_expandable_grab_D_alt:NNnwNn #1#2#3#4 \q__xparse #5#6
+  { #2 { \__xparse_expandable_grab_D_alt:NNwNn #1 \q__xparse #2 } }
+\cs_set_protected:Npn \__xparse_tmp:w #1
   {
-    \str_if_eq:onTF
-      { #1 { } #6 #2 #2 }
-      { { } #2 }
+    \cs_new:Npn \__xparse_expandable_grab_D_alt:NNwNn ##1##2##3 \q__xparse ##4##5
       {
-        #1
-          { \__xparse_expandable_grab_D_alt:Nwn #5 #4 \q__xparse }
-          #6 \ERROR
+        \str_if_eq:onTF
+          { ##1 { } ##5 ##2 ##2 }
+          { { } ##2 }
+          {
+            ##1
+              { \__xparse_expandable_grab_D_alt:Nwn ##4 ##3 \q__xparse }
+              ##5 \ERROR
+          }
+          { ##3 {#1} \q__xparse ##4 {##5} }
       }
-      { #4 {#3} \q__xparse #5 {#6} }
   }
+\exp_args:No \__xparse_tmp:w { \c__xparse_no_value_tl }
 \cs_new:Npn \__xparse_expandable_grab_D_alt:Nwn #1#2 \q__xparse #3
   {
     \tl_if_blank:oTF { \use_none:n #3 }
@@ -1239,46 +1428,85 @@
       }
         #2 \q__xparse #1
   }
+\cs_new:Npn \__xparse_expandable_grab_E:w #1 \q__xparse #2
+  { #2 { \__xparse_expandable_grab_E_test:nnwn #1 \q__xparse #2 } }
+\cs_new:Npn \__xparse_expandable_grab_E_test:nnwn #1#2#3 \q__xparse #4#5
+  {
+    \__xparse_expandable_grab_E_loop:nnnNNw {#5} { } { }
+      #1 \q_nil \q_nil \q_nil \q_mark #2 \q_nil
+    #3 \q__xparse #4
+  }
+\cs_new:Npn \__xparse_expandable_grab_E_loop:nnnNNw
+    #1#2#3#4#5#6 \q_nil #7 \q_mark #8
+  {
+    \quark_if_nil:NTF #4
+      { \__xparse_expandable_grab_E_end:nnw {#1} {#3} }
+      {
+        \__xparse_if_no_value:nTF {#8}
+          { \str_if_eq:onTF { #4 { } #1 #5 } {#5} }
+          { \use_ii:nn }
+            { \__xparse_expandable_grab_E_aux:w { #2 #4 #5 #6 } {#3} ~ }
+            {
+              \__xparse_expandable_grab_E_loop:nnnNNw
+                {#1} { #2 #4 #5 } { #3 {#8} }
+                #6 \q_nil #7 \q_mark
+            }
+      }
+  }
+\cs_new:Npn \__xparse_expandable_grab_E_aux:w #1 \q__xparse #2
+  { #2 { \__xparse_expandable_grab_E_aux:nnw #1 \q__xparse #2 } }
+\cs_new:Npn \__xparse_expandable_grab_E_aux:nnw #1#2#3 \q_nil #4 \q__xparse #5#6
+  { \__xparse_expandable_grab_E:w {#1} { #2 {#6} #3 } #4 \q__xparse #5 }
+\cs_new:Npn \__xparse_expandable_grab_E_end:nnw #1#2#3 \q__xparse #4
+  { #3 {#2} \q__xparse #4 {#1} }
 \cs_new:Npn \__xparse_expandable_grab_m:w #1 \q__xparse #2
   { #2 { \__xparse_expandable_grab_m_aux:wNn #1 \q__xparse #2 } }
 \cs_new:Npn \__xparse_expandable_grab_m_aux:wNn #1 \q__xparse #2#3
   { #1 {#3} \q__xparse #2 }
 \cs_new:Npn \__xparse_expandable_grab_R:w #1 \q__xparse #2
-  { #2 { \__xparse_expandable_grab_R_aux:NNNnwNn #1 \q__xparse #2 } }
-\cs_new:Npn \__xparse_expandable_grab_R_aux:NNNnwNn #1#2#3#4#5 \q__xparse #6#7
+  { #2 { \__xparse_expandable_grab_R_aux:NNNwNn #1 \q__xparse #2 } }
+\cs_set_protected:Npn \__xparse_tmp:w #1
   {
-    \str_if_eq:onTF
-      { #1 { } { } #7 #2 \q__xparse #3 }
-      { { } {#2} { } }
-      {
-        #1
-          { \__xparse_expandable_grab_D:NNNwNnnn #1#2#3#5 \q__xparse #6 }
-          \q_nil { } #2 \ERROR \q__xparse \ERROR
-      }
+    \cs_new:Npn \__xparse_expandable_grab_R_aux:NNNwNn ##1##2##3##4 \q__xparse ##5##6
       {
-        \__msg_kernel_expandable_error:nnn
-          { xparse } { missing-required } {#2}
-        #5 {#4} \q__xparse #6 {#7}
+        \str_if_eq:onTF
+          { ##1 { } { } ##6 ##2 \q__xparse ##3 }
+          { { } {##2} { } }
+          {
+            ##1
+              { \__xparse_expandable_grab_D:NNNwNnnn ##1##2##3##4 \q__xparse ##5 }
+              \q_nil { } ##2 \ERROR \q__xparse \ERROR
+          }
+          {
+            \__msg_kernel_expandable_error:nnnn
+              { xparse } { missing-required } {##5} {##2}
+            ##4 {#1} \q__xparse ##5 {##6}
+          }
       }
   }
+\exp_args:No \__xparse_tmp:w { \c__xparse_no_value_tl }
 \cs_new:Npn \__xparse_expandable_grab_R_alt:w #1 \q__xparse #2
   { #2 { \__xparse_expandable_grab_R_alt_aux:NNnwNn #1 \q__xparse #2 } }
-\cs_new:Npn \__xparse_expandable_grab_R_alt_aux:NNnwNn #1#2#3#4 \q__xparse #5#6
+\cs_set_protected:Npn \__xparse_tmp:w #1
   {
-    \str_if_eq:onTF
-      { #1 { } #6 #2 #2 }
-      { { } #2 }
-      {
-        #1
-          { \__xparse_expandable_grab_D_alt:Nwn #5 #4 \q__xparse }
-          #6 \ERROR
-      }
+    \cs_new:Npn \__xparse_expandable_grab_R_alt_aux:NNwNn ##1##2##3 \q__xparse ##4##5
       {
-        \__msg_kernel_expandable_error:nnn
-          { xparse } { missing-required } {#2}
-        #4 {#3} \q__xparse #5 {#6}
+        \str_if_eq:onTF
+          { ##1 { } ##5 ##2 ##2 }
+          { { } ##2 }
+          {
+            ##1
+              { \__xparse_expandable_grab_D_alt:Nwn ##4 ##3 \q__xparse }
+              ##5 \ERROR
+          }
+          {
+            \__msg_kernel_expandable_error:nnnn
+              { xparse } { missing-required } {##4} {##2}
+            ##3 {#1} \q__xparse ##4 {##5}
+          }
       }
   }
+\exp_args:No \__xparse_tmp:w { \c__xparse_no_value_tl }
 \cs_new:Npn \__xparse_expandable_grab_t:w #1 \q__xparse #2
   { #2 { \__xparse_expandable_grab_t_aux:NNwn #1 \q__xparse #2 } }
 \cs_new:Npn \__xparse_expandable_grab_t_aux:NNwn #1#2#3 \q__xparse #4#5
@@ -1289,14 +1517,6 @@
   }
 \cs_new:Npn \__xparse_put_arg_expandable:nw #1#2 \q__xparse { #2 {#1} \q__xparse }
 \cs_generate_variant:Nn \__xparse_put_arg_expandable:nw { o }
-\cs_new:Npn \__xparse_grab_expandable_end:wN #1 \q__xparse #2 {#1}
-\cs_new_protected:Npn \__xparse_process_arg:n #1
-  {
-    \int_incr:N \l__xparse_processor_int
-    \cs_set_protected:cpx
-      { __xparse_processor_ \int_use:N \l__xparse_processor_int :n } ##1
-      { \exp_not:n {#1} {##1} }
-  }
 \cs_new_protected:Npn \__xparse_bool_reverse:N #1
   {
     \bool_if:NTF #1
@@ -1407,30 +1627,38 @@
           { \tl_to_str:n {#1} }
       }
   }
+\cs_new_protected:Npn \__xparse_get_arg_spec:NTF #1#2#3
+  {
+    \__xparse_cmd_if_xparse:NTF #1
+      {
+        \tl_set:Nx \ArgumentSpecification { \tl_item:Nn #1 { 2 } }
+        #2
+      }
+      {#3}
+  }
 \cs_new_protected:Npn \__xparse_get_arg_spec:N #1
   {
-    \prop_get:NnNF \l__xparse_command_arg_specs_prop {#1}
-      \ArgumentSpecification
+    \__xparse_get_arg_spec:NTF #1 { }
       { \__xparse_get_arg_spec_error:N #1 }
   }
 \cs_new_protected:Npn \__xparse_get_arg_spec:n #1
   {
-    \prop_get:NnNF \l__xparse_environment_arg_specs_prop {#1}
-      \ArgumentSpecification
+    \exp_args:Nc \__xparse_get_arg_spec:NTF
+      { environment~ \tl_to_str:n {#1} }
+      { }
       { \__xparse_get_arg_spec_error:n {#1} }
   }
 \tl_new:N \ArgumentSpecification
 \cs_new_protected:Npn \__xparse_show_arg_spec:N #1
   {
-    \prop_get:NnNTF \l__xparse_command_arg_specs_prop {#1}
-      \ArgumentSpecification
+    \__xparse_get_arg_spec:NTF #1
       { \tl_show:N \ArgumentSpecification }
       { \__xparse_get_arg_spec_error:N #1 }
   }
 \cs_new_protected:Npn \__xparse_show_arg_spec:n #1
   {
-    \prop_get:NnNTF \l__xparse_environment_arg_specs_prop {#1}
-      \ArgumentSpecification
+    \exp_args:Nc \__xparse_get_arg_spec:NTF
+      { environment~ \tl_to_str:n {#1} }
       { \tl_show:N \ArgumentSpecification }
       { \__xparse_get_arg_spec_error:n {#1} }
   }
@@ -1483,8 +1711,50 @@
       }
     }
 \group_end:
+\cs_new:Npn \__xparse_tl_mapthread_function:NNN #1#2#3
+  {
+    \exp_after:wN \exp_after:wN
+    \exp_after:wN \__xparse_tl_mapthread_loop:w
+    \exp_after:wN \exp_after:wN
+    \exp_after:wN #3
+    \exp_after:wN #1
+    \exp_after:wN \q_recursion_tail
+    \exp_after:wN \q_mark
+    #2
+    \q_recursion_tail
+    \q_recursion_stop
+  }
+\cs_new:Npn \__xparse_tl_mapthread_function:nnN #1#2#3
+  {
+    \__xparse_tl_mapthread_loop:w #3
+      #1 \q_recursion_tail \q_mark
+      #2 \q_recursion_tail \q_recursion_stop
+  }
+\cs_new:Npn \__xparse_tl_mapthread_loop:w #1#2#3 \q_mark #4
+  {
+    \quark_if_recursion_tail_stop:n {#2}
+    \quark_if_recursion_tail_stop:n {#4}
+    #1 {#2} {#4}
+    \__xparse_tl_mapthread_loop:w #1#3 \q_mark
+  }
+\cs_new_protected:Npn \__xparse_cmd_if_xparse:NTF #1
+  {
+    \exp_args:Nf \str_case_x:nnTF
+      {
+        \exp_args:Nf \tl_if_empty:nT { \token_get_arg_spec:N #1 }
+          {
+            \exp_last_unbraced:Nf \__xparse_cmd_if_xparse_aux:w
+              { \token_get_replacement_spec:N #1 } ~ \q_stop
+          }
+      }
+      {
+        { \token_to_str:N \__xparse_start:nNNnnn } { }
+        { \token_to_str:N \__xparse_start_expandable:nNNNn } { }
+      }
+  }
+\cs_new:Npn \__xparse_cmd_if_xparse_aux:w #1 ~ #2 \q_stop {#1}
 \__msg_kernel_new:nnnn { xparse } { bad-arg-spec }
-  { Bad~argument~specification~'#1'. }
+  { Bad~argument~specification~'#2'~for~command~'#1'. }
   {
     \c__msg_coding_error_text_tl
     The~argument~specification~provided~was~not~valid:~
@@ -1521,7 +1791,8 @@
   }
 \__msg_kernel_new:nnnn { xparse } { expandable-ending-optional }
   {
-    Argument~specification~for~expandable~command~ends~with~optional~argument.
+    Argument~specification~'#2'~for~expandable~command~'#1'~
+    ends~with~optional~argument.
   }
   {
     \c__msg_coding_error_text_tl
@@ -1530,27 +1801,33 @@
     argument~with~expandable~commands.
   }
 \__msg_kernel_new:nnnn { xparse } { inconsistent-long }
-  { Inconsistent~long~arguments~for~expandable~command. }
+  { Inconsistent~long~arguments~for~expandable~command~'#1'. }
   {
     \c__msg_coding_error_text_tl
     The~arguments~for~an~expandable~command~must~either~all~be~
     short~or~all~be~long.~You~have~tried~to~mix~the~two~types.
   }
 \__msg_kernel_new:nnnn { xparse } { invalid-expandable-argument-type }
-  { Argument~type~'#1'~not~available~for~an~expandable~function. }
+  { Argument~type~'#2'~not~available~for~expandable~command~'#1'. }
   {
     \c__msg_coding_error_text_tl
-    The~letter~'#1'~does~not~specify~an~argument~type~which~can~be~used~
-    in~an~expandable~function.
+    The~letter~'#2'~does~not~specify~an~argument~type~which~can~be~used~
+    in~an~expandable~command.
     \\ \\
-    LaTeX~will~assume~you~want~a~standard~mandatory~argument~(type~'m').
+    LaTeX~will~ignore~this~entire~definition.
+  }
+\__msg_kernel_new:nnnn { xparse } { loop-in-defaults }
+  { Circular~dependency~in~defaults~of~'#1'. }
+  {
+    \c__msg_coding_error_text_tl
+    The~default~values~of~two~or~more~arguments~of~'#1'~depend~on~each~
+    other~in~a~way~that~cannot~be~resolved.
   }
 \__msg_kernel_new:nnnn { xparse } { missing-required }
-  { Failed~to~find~required~argument~starting~with~'#1'. }
+  { Failed~to~find~required~argument~starting~with~'#2'~for~command~'#1'. }
   {
-    There~is~supposed~to~be~an~argument~to~the~current~function~starting~with~
-    '#1'.~LaTeX~did~not~find~it,~and~will~insert~'#2'~as~the~value~to~be~
-    processed.
+    The~current~command~'#1'~expects~an~argument~starting~with~'#2'.~
+    LaTeX~did~not~find~it,~and~will~insert~a~default~value~to~be~processed.
   }
 \__msg_kernel_new:nnnn { xparse } { non-xparse-command }
   { Command~'#1'~not~defined~using~xparse. }
@@ -1585,19 +1862,20 @@
     LaTeX~will~ignore~this~entire~definition.
   }
 \__msg_kernel_new:nnnn { xparse } { not-single-token }
-  { Argument~delimiter~should~be~a~single~token:~'#1'. }
+  { Argument~delimiter~'#2'~for~the~command~'#1'~should~be~a~single~token. }
   {
     \c__msg_coding_error_text_tl
     The~argument~specification~provided~was~not~valid:~
-    in~a~place~where~a~single~token~is~required,~LaTeX~found~'#1'. \\ \\
+    in~a~place~where~a~single~token~is~required,~LaTeX~found~'#2'. \\ \\
     LaTeX~will~ignore~this~entire~definition.
   }
 \__msg_kernel_new:nnnn { xparse } { processor-in-expandable }
-  { Argument~processors~cannot~be~used~with~expandable~functions. }
+  { Argument~processor~'>{#2}'~cannot~be~used~for~the~expandable~command~'#1'. }
   {
     \c__msg_coding_error_text_tl
     The~argument~specification~for~#1~contains~a~processor~function:~
-    this~is~only~supported~for~standard~robust~functions.
+    this~is~only~supported~for~standard~robust~commands. \\ \\
+    LaTeX~will~ignore~this~entire~definition.
   }
 \__msg_kernel_new:nnnn { xparse } { split-excess-tokens }
   { Too~many~'#1'~tokens~when~trying~to~split~argument. }
@@ -1606,12 +1884,20 @@
     at~each~occurrence~of~the~token~'#1',~up~to~a~maximum~of~#2~parts.~
     There~were~too~many~'#1'~tokens.
   }
+\__msg_kernel_new:nnnn { xparse } { too-many-arguments }
+  { Too~many~arguments~in~argument~specification~'#2'~of~command~'#1'. }
+  {
+    \c__msg_coding_error_text_tl
+    The~argument~specification~provided~has~more~than~9~arguments.~
+    This~cannot~be~implemented. \\ \\
+    LaTeX~will~ignore~this~entire~definition.
+  }
 \__msg_kernel_new:nnnn { xparse } { unknown-argument-type }
-  { Unknown~argument~type~'#1'~replaced~by~'m'. }
+  { Unknown~argument~type~'#2'~for~the~command~'#1'. }
   {
     \c__msg_coding_error_text_tl
-    The~letter~'#1'~does~not~specify~a~known~argument~type.~
-    LaTeX~will~assume~you~want~a~standard~mandatory~argument~(type~'m').
+    The~letter~'#2'~does~not~specify~a~known~argument~type.~
+    LaTeX~will~ignore~this~entire~definition.
   }
 \__msg_kernel_new:nnnn { xparse } { unknown-command }
   { Unknown~document~command~'#1'. }
@@ -1666,6 +1952,12 @@
     Redefining~environment~'#1'~
     with~sig.~'#2'~\msg_line_context:.
   }
+\__msg_kernel_new:nnn { xparse } { optional-mandatory }
+  {
+    Since~the~mandatory~argument~'#1'~has~the~same~delimiter~'#2'~
+    as~a~previous~optional~argument,~it~will~not~be~possible~to~
+    omit~all~optional~arguments~when~calling~this~command.
+  }
 \cs_new_eq:NN \BooleanFalse \c_false_bool
 \cs_new_eq:NN \BooleanTrue  \c_true_bool
 \cs_new_protected:Npn \DeclareDocumentCommand #1#2#3