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+% \iffalse meta-comment
+%
+%% File: l3backend-draw.dtx
+%
+% Copyright (C) 2019 The LaTeX3 Project
+%
+% It may be distributed and/or modified under the conditions of the
+% LaTeX Project Public License (LPPL), either version 1.3c of this
+% license or (at your option) any later version.  The latest version
+% of this license is in the file
+%
+%    https://www.latex-project.org/lppl.txt
+%
+% This file is part of the "l3backend bundle" (The Work in LPPL)
+% and all files in that bundle must be distributed together.
+%
+% -----------------------------------------------------------------------
+%
+% The development version of the bundle can be found at
+%
+%    https://github.com/latex3/latex3
+%
+% for those people who are interested.
+%
+%<*driver>
+\documentclass[full,kernel]{l3doc}
+\begin{document}
+  \DocInput{\jobname.dtx}
+\end{document}
+%</driver>
+% \fi
+%
+% \title{^^A
+%   The \textsf{l3backend-draw} package\\ Backend drawing support^^A
+% }
+%
+% \author{^^A
+%  The \LaTeX3 Project\thanks
+%    {^^A
+%      E-mail:
+%        \href{mailto:latex-team@latex-project.org}
+%          {latex-team@latex-project.org}^^A
+%    }^^A
+% }
+%
+% \date{Released 2019-08-25}
+%
+% \maketitle
+%
+% \begin{documentation}
+%
+% \end{documentation}
+%
+% \begin{implementation}
+%
+% \section{\pkg{l3backend-draw} Implementation}
+%
+%    \begin{macrocode}
+%<*initex|package>
+%<@@=draw>
+%    \end{macrocode}
+%
+% \subsection{\texttt{dvips} backend}
+%
+%    \begin{macrocode}
+%<*dvips>
+%    \end{macrocode}
+%
+% \begin{macro}{\@@_backend_literal:n, \@@_backend_literal:x}
+%   The same as literal PostScript: same arguments about positioning apply
+%   her.
+%    \begin{macrocode}
+\cs_new_eq:NN \@@_backend_literal:n \__kernel_backend_literal_postscript:n
+\cs_generate_variant:Nn \@@_backend_literal:n { x }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_begin:, \@@_backend_end:}
+% \begin{macro}{color.fc}
+%   The |ps::[begin]| special here deals with positioning but allows us to
+%   continue on to a matching |ps::[end]|: contrast with |ps:|, which positions
+%   but where we can't split material between separate calls. The
+%   |@beginspecial|/|@endspecial| pair are from |special.pro| and correct the
+%   scale and $y$-axis direction. The definition of |/color.fc| deals with fill
+%   color in paths. In contrast to \pkg{pgf}, we don't save the current point:
+%   discussion with Tom Rokici suggested a better way to handle the necessary
+%   translations (see \cs{@@_backend_box_use:Nnnnn}). (Note that
+%   |@beginspecial|/|@endspecial| forms a backend scope.) The  |[begin]|/^^A
+%   |[end]| lines are handled differently from the rest as they are
+%   conceptually different: not really drawing literals but instructions to
+%   \texttt{dvips} itself.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_begin:
+  {
+    \__kernel_backend_literal:n { ps::[begin] }
+    \@@_backend_literal:n { @beginspecial }
+    \@@_backend_literal:n { SDict ~ begin ~ /color.fc ~ { } ~ def ~ end }
+  }
+\cs_new_protected:Npn \@@_backend_end:
+  {
+    \@@_backend_literal:n { @endspecial }
+    \__kernel_backend_literal:n { ps::[end] }
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_scope_begin:, \@@_backend_scope_end:}
+%   Scope here may need to contain saved definitions, so the entire memory
+%   rather than just the graphic state has to be sent to the stack.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_scope_begin:
+  { \@@_backend_literal:n { save } }
+\cs_new_protected:Npn \@@_backend_scope_end:
+  { \@@_backend_literal:n { restore } }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_moveto:nn, \@@_backend_lineto:nn}
+% \begin{macro}{\@@_backend_rectangle:nnnn}
+% \begin{macro}{\@@_backend_curveto:nnnnnn}
+%   Path creation operations mainly resolve directly to PostScript primitive
+%   steps, with only the need to convert to \texttt{bp}. Notice that
+%   \texttt{x}-type expansion is included here to ensure that any variable
+%   values are forced to literals before any possible caching. There is
+%   no native rectangular path command (without also clipping, filling or
+%   stroking), so that task is done using a small amount of PostScript.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_moveto:nn #1#2
+  {
+    \@@_backend_literal:x
+      {
+        \dim_to_decimal_in_bp:n {#1} ~ 
+        \dim_to_decimal_in_bp:n {#2} ~ moveto
+      }
+  }
+\cs_new_protected:Npn \@@_backend_lineto:nn #1#2
+  {
+    \@@_backend_literal:x
+      {
+        \dim_to_decimal_in_bp:n {#1} ~
+        \dim_to_decimal_in_bp:n {#2} ~ lineto
+      }
+  }
+\cs_new_protected:Npn \@@_backend_rectangle:nnnn #1#2#3#4
+  {
+     \@@_backend_literal:x
+       {
+         \dim_to_decimal_in_bp:n {#4} ~ \dim_to_decimal_in_bp:n {#3} ~
+         \dim_to_decimal_in_bp:n {#1} ~ \dim_to_decimal_in_bp:n {#2} ~
+         moveto~dup~0~rlineto~exch~0~exch~rlineto~neg~0~rlineto~closepath
+      }
+  }
+\cs_new_protected:Npn \@@_backend_curveto:nnnnnn #1#2#3#4#5#6
+  {
+    \@@_backend_literal:x
+      {
+        \dim_to_decimal_in_bp:n {#1} ~ \dim_to_decimal_in_bp:n {#2} ~
+        \dim_to_decimal_in_bp:n {#3} ~ \dim_to_decimal_in_bp:n {#4} ~
+        \dim_to_decimal_in_bp:n {#5} ~ \dim_to_decimal_in_bp:n {#6} ~
+        curveto
+      }
+ }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_evenodd_rule:, \@@_backend_nonzero_rule:}
+% \begin{variable}{\g_@@_draw_eor_bool}
+%    The even-odd rule here can be implemented as a simply switch.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_evenodd_rule:
+  { \bool_gset_true:N \g_@@_draw_eor_bool }
+\cs_new_protected:Npn \@@_backend_nonzero_rule:
+  { \bool_gset_false:N \g_@@_draw_eor_bool }
+\bool_new:N \g_@@_draw_eor_bool
+%    \end{macrocode}
+% \end{variable}
+% \end{macro}
+%
+% \begin{macro}
+%   {
+%     \@@_backend_closepath:   ,
+%     \@@_backend_stroke:      ,
+%     \@@_backend_closestroke: ,
+%     \@@_backend_fill:        ,
+%     \@@_backend_fillstroke:  ,
+%     \@@_backend_clip:        ,
+%     \@@_backend_discardpath:
+%   }
+% \begin{variable}{\g_@@_draw_clip_bool}
+%   Unlike PDF, PostScript doesn't track separate colors for strokes and other
+%   elements. It is also desirable to have the |clip| keyword after a stroke or
+%   fill. To achieve those outcomes, there is some work to do. For color, the
+%   stoke color is simple but the fill one has to be inserted by hand. For
+%   clipping, the required ordering is achieved using a \TeX{} switch. All of
+%   the operations end with a new path instruction  as they do not terminate
+%   (again in contrast to PDF).
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_closepath:
+  { \@@_backend_literal:n { closepath } }
+\cs_new_protected:Npn \@@_backend_stroke:
+  {
+    \@@_backend_literal:n { stroke }
+    \bool_if:NT \g_@@_draw_clip_bool
+      {
+        \@@_backend_literal:x
+          {
+            \bool_if:NT \g_@@_draw_eor_bool { eo }
+            clip
+          }
+      }
+    \@@_backend_literal:n { newpath }
+    \bool_gset_false:N \g_@@_draw_clip_bool
+  }
+\cs_new_protected:Npn \@@_backend_closestroke:
+  {
+    \@@_backend_closepath:
+    \@@_backend_stroke:
+  }
+\cs_new_protected:Npn \@@_backend_fill:
+  {
+    \@@_backend_literal:n { gsave }
+    \@@_backend_literal:n { color.fc }
+    \@@_backend_literal:x
+      {
+        \bool_if:NT \g_@@_draw_eor_bool { eo }
+        fill
+      }
+    \@@_backend_literal:n { grestore }
+    \bool_if:NT \g_@@_draw_clip_bool
+      {
+        \@@_backend_literal:x
+          {
+            \bool_if:NT \g_@@_draw_eor_bool { eo }
+            clip
+          }
+      }
+    \@@_backend_literal:n { newpath }
+    \bool_gset_false:N \g_@@_draw_clip_bool
+  }
+\cs_new_protected:Npn \@@_backend_fillstroke:
+  {
+    \@@_backend_literal:n { gsave }
+    \@@_backend_literal:n { color.fc }
+    \@@_backend_literal:x
+      {
+        \bool_if:NT \g_@@_draw_eor_bool { eo }
+        fill
+      }
+    \@@_backend_literal:n { grestore }
+    \@@_backend_literal:n { stroke }
+    \bool_if:NT \g_@@_draw_clip_bool
+      {
+        \@@_backend_literal:x
+          {
+            \bool_if:NT \g_@@_draw_eor_bool { eo }
+            clip
+          }
+      }
+    \@@_backend_literal:n { newpath }
+    \bool_gset_false:N \g_@@_draw_clip_bool
+  }
+\cs_new_protected:Npn \@@_backend_clip:
+  { \bool_gset_true:N \g_@@_draw_clip_bool }
+\bool_new:N \g_@@_draw_clip_bool
+\cs_new_protected:Npn \@@_backend_discardpath:
+  {
+    \bool_if:NT \g_@@_draw_clip_bool
+      {
+        \@@_backend_literal:x
+          {
+            \bool_if:NT \g_@@_draw_eor_bool { eo }
+            clip
+          }
+      }
+    \@@_backend_literal:n { newpath }
+    \bool_gset_false:N \g_@@_draw_clip_bool
+  }
+%    \end{macrocode}
+% \end{variable}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_dash_pattern:nn}
+% \begin{macro}{\@@_backend_dash:n}
+% \begin{macro}{\@@_backend_linewidth:n}
+% \begin{macro}{\@@_backend_miterlimit:n}
+% \begin{macro}
+%   {
+%     \@@_backend_cap_butt:, \@@_backend_cap_round:, \@@_backend_cap_rectangle:,
+%     \@@_backend_join_miter:, \@@_backend_join_round:, \@@_backend_join_bevel:
+%   }
+%   Converting paths to output is again a case of mapping directly to
+%   PostScript operations.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_dash_pattern:nn #1#2
+  {
+    \@@_backend_literal:x
+      {
+        [ 
+          \exp_args:Nf \use:n
+            { \clist_map_function:nN {#1} \@@_backend_dash:n }
+        ] ~
+        \dim_to_decimal_in_bp:n {#2} ~ setdash
+      }
+  }
+\cs_new:Npn \@@_backend_dash:n #1
+  { ~ \dim_to_decimal_in_bp:n {#1} }
+\cs_new_protected:Npn \@@_backend_linewidth:n #1
+  {
+    \@@_backend_literal:x
+      { \dim_to_decimal_in_bp:n {#1} ~ setlinewidth }
+  }
+\cs_new_protected:Npn \@@_backend_miterlimit:n #1
+  { \@@_backend_literal:x { \fp_eval:n {#1} ~ setmiterlimit } }
+\cs_new_protected:Npn \@@_backend_cap_butt:
+  { \@@_backend_literal:n { 0 ~ setlinecap } }
+\cs_new_protected:Npn \@@_backend_cap_round:
+  { \@@_backend_literal:n { 1 ~ setlinecap } }
+\cs_new_protected:Npn \@@_backend_cap_rectangle:
+  { \@@_backend_literal:n { 2 ~ setlinecap } }
+\cs_new_protected:Npn \@@_backend_join_miter:
+  { \@@_backend_literal:n { 0 ~ setlinejoin } }
+\cs_new_protected:Npn \@@_backend_join_round:
+  { \@@_backend_literal:n { 1 ~ setlinejoin } }
+\cs_new_protected:Npn \@@_backend_join_bevel:
+  { \@@_backend_literal:n { 2 ~ setlinejoin } }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}
+%   {
+%     \@@_backend_color_fill_cmyk:nnnn   ,
+%     \@@_backend_color_stroke_cmyk:nnnn
+%   }
+% \begin{macro}
+%   {
+%     \@@_backend_color_fill_gray:n   ,
+%     \@@_backend_color_stroke_gray:n
+%   }
+% \begin{macro}
+%   {
+%     \@@_backend_color_fill_rgb:nnn   ,
+%     \@@_backend_color_stroke_rgb:nnn
+%   }
+% \begin{macro}
+%   {
+%     \@@_backend_color_fill:n, \@@_backend_color_fill:x,
+%     \@@_backend_color_stroke:n, \@@_backend_color_stroke:x
+%   }
+%   For \texttt{dvips}, we can use the standard color stack to deal with
+%   stroke color, but for fills have to switch to raw PostScript. This is
+%   thus not handled by the stack, but the context is very restricted. See
+%   also how fills are implemented.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_color_fill_cmyk:nnnn #1#2#3#4
+  {
+    \@@_backend_color_fill:x
+      {
+        \fp_eval:n {#1} ~ \fp_eval:n {#2} ~
+        \fp_eval:n {#3} ~ \fp_eval:n {#4} ~
+        setcmykcolor
+      }
+  }
+\cs_new_protected:Npn \@@_backend_color_stroke_cmyk:nnnn #1#2#3#4
+  {
+    \@@_backend_color_stroke:x
+      {
+        cmyk ~
+        \fp_eval:n {#1} ~ \fp_eval:n {#2} ~
+        \fp_eval:n {#3} ~ \fp_eval:n {#4}
+      }
+  }
+\cs_new_protected:Npn \@@_backend_color_fill_gray:n #1
+  { \@@_backend_color_fill:x { \fp_eval:n {#1} ~ setgray } }
+\cs_new_protected:Npn \@@_backend_color_stroke_gray:n #1
+  { \@@_backend_color_stroke:x { gray ~ \fp_eval:n {#1} } }
+\cs_new_protected:Npn \@@_backend_color_fill_rgb:nnn #1#2#3
+  {
+    \@@_backend_color_fill:x
+      { \fp_eval:n {#1} ~ \fp_eval:n {#2} ~ \fp_eval:n {#3} ~ setrgbcolor }
+  }
+\cs_new_protected:Npn \@@_backend_color_stroke_rgb:nnn #1#2#3
+  {
+    \@@_backend_color_stroke:x
+      { rgb ~ \fp_eval:n {#1} ~ \fp_eval:n {#2} ~ \fp_eval:n {#3} }
+  }
+\cs_new_protected:Npn \@@_backend_color_fill:n #1
+  { 
+    \__kernel_backend_postscript:n
+      { SDict ~ begin ~ /color.fc ~ { #1 } ~ def ~ end }
+  }
+\cs_generate_variant:Nn \@@_backend_color_fill:n { x }
+\cs_new_protected:Npn \@@_backend_color_stroke:n #1
+  {
+    \__kernel_backend_literal:n { color~push~#1 } 
+    \group_insert_after:N \@@_color_reset:
+  }
+\cs_generate_variant:Nn \@@_backend_color_stroke:n { x }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_cm:nnnn}
+%   In \texttt{dvips}, keeping the transformations in line with the engine
+%   is unfortunately not possible for scaling and rotations: even if we
+%   decompose the matrix into those operations, there is still no backend
+%   tracking (\emph{cf.}~\texttt{(x)dvipdfmx}). Thus we take the shortest
+%   path available and simply dump the matrix as given.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_cm:nnnn #1#2#3#4
+  {
+    \@@_backend_literal:n
+      {
+        [
+          \fp_eval:n {#1} ~ \fp_eval:n {#2} ~
+          \fp_eval:n {#3} ~ \fp_eval:n {#4} ~
+          0 ~ 0
+        ] ~
+        concat
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_box_use:Nnnnn}
+%   Inside a picture |@beginspecial|/|@endspecial| are active, which is
+%   normally a good thing but means that the position and scaling would be off
+%   if the box was inserted directly. To deal with that, there are a number of
+%   possible approaches. The implementation here was suggested by Tom Rokici
+%   (author of \texttt{dvips}). We end the current special placement, then
+%   set the current point with a literal |[begin]|. As for general
+%   literals, we then use the stack to store the current point and move to
+%   it. To insert the required transformation, we have to flip the $y$-axis,
+%   once before and once after it. Then we get back to the \TeX{} reference
+%   point to insert our content. The clean up has to happen in the right
+%   places, hence the |[begin]|/|[end]| pair around |restore|. Finally,
+%   we can return to \enquote{normal} drawing mode. Notice that the set up
+%   here is very similar to that in \cs{@@_align_currentpoint_\ldots}, but
+%   the ordering of saving and restoring is different (intermixed).
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_box_use:Nnnnn #1#2#3#4#5
+  {
+    \@@_backend_literal:n { @endspecial }
+    \@@_backend_literal:n { [end] }
+    \@@_backend_literal:n { [begin] }
+    \@@_backend_literal:n { save }
+    \@@_backend_literal:n { currentpoint }
+    \@@_backend_literal:n { currentpoint~translate }
+    \@@_backend_cm:nnnn { 1 } { 0 } { 0 } { -1 }
+    \@@_backend_cm:nnnn {#2} {#3} {#4} {#5}
+    \@@_backend_cm:nnnn { 1 } { 0 } { 0 } { -1 }
+    \@@_backend_literal:n { neg~exch~neg~exch~translate }
+    \@@_backend_literal:n { [end] }
+    \hbox_overlap_right:n { \box_use:N #1 }
+    \@@_backend_literal:n { [begin] }
+    \@@_backend_literal:n { restore }
+    \@@_backend_literal:n { [end] }
+    \@@_backend_literal:n { [begin] }
+    \@@_backend_literal:n { @beginspecial }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%    \begin{macrocode}
+%</dvips>
+%    \end{macrocode}
+%
+% \subsection{\texttt{pdfmode} and \texttt{(x)dvipdfmx}}
+%
+% Both \texttt{pdfmode} and \texttt{(x)dvipdfmx} directly produce PDF output
+% and understand a shared set of specials for drawing commands.
+%
+%    \begin{macrocode}
+%<*dvipdfmx|pdfmode|xdvipdfmx>
+%    \end{macrocode}
+%
+% \subsubsection{Drawing}
+%
+% \begin{macro}{\@@_backend_literal:n, \@@_backend_literal:x}
+%   Pass data through using a dedicated interface.
+%    \begin{macrocode}
+\cs_new_eq:NN \@@_backend_literal:n \__kernel_backend_literal_pdf:n
+\cs_generate_variant:Nn \@@_backend_literal:n { x }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_begin:, \@@_backend_end:}
+%   No special requirements here, so simply set up a drawing scope.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_begin:
+  { \@@_backend_scope_begin: }
+\cs_new_protected:Npn \@@_backend_end:
+  { \@@_backend_scope_end: }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_scope_begin:, \@@_backend_scope_end:}
+%   Use the backend-level scope mechanisms.
+%    \begin{macrocode}
+\cs_new_eq:NN \@@_backend_scope_begin: \__kernel_backend_scope_begin:
+\cs_new_eq:NN \@@_backend_scope_end: \__kernel_backend_scope_end:
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_moveto:nn, \@@_backend_lineto:nn}
+% \begin{macro}{\@@_backend_curveto:nnnnnn}
+% \begin{macro}{\@@_backend_rectangle:nnnn}
+%   Path creation operations all resolve directly to PDF primitive steps, with
+%   only the need to convert to \texttt{bp}.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_moveto:nn #1#2
+  {
+    \@@_backend_literal:x
+      { \dim_to_decimal_in_bp:n {#1} ~ \dim_to_decimal_in_bp:n {#2} ~ m }
+  }
+\cs_new_protected:Npn \@@_backend_lineto:nn #1#2
+  {
+    \@@_backend_literal:x
+      { \dim_to_decimal_in_bp:n {#1} ~ \dim_to_decimal_in_bp:n {#2} ~ l }
+  }
+\cs_new_protected:Npn \@@_backend_curveto:nnnnnn #1#2#3#4#5#6
+  {
+    \@@_backend_literal:x
+      {
+        \dim_to_decimal_in_bp:n {#1} ~ \dim_to_decimal_in_bp:n {#2} ~
+        \dim_to_decimal_in_bp:n {#3} ~ \dim_to_decimal_in_bp:n {#4} ~
+        \dim_to_decimal_in_bp:n {#5} ~ \dim_to_decimal_in_bp:n {#6} ~
+        c
+      }
+ }
+\cs_new_protected:Npn \@@_backend_rectangle:nnnn #1#2#3#4
+  {
+     \@@_backend_literal:x
+      {
+        \dim_to_decimal_in_bp:n {#1} ~ \dim_to_decimal_in_bp:n {#2} ~
+        \dim_to_decimal_in_bp:n {#3} ~ \dim_to_decimal_in_bp:n {#4} ~
+        re
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_evenodd_rule:, \@@_backend_nonzero_rule:}
+% \begin{variable}{\g_@@_draw_eor_bool}
+%    The even-odd rule here can be implemented as a simply switch.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_evenodd_rule:
+  { \bool_gset_true:N \g_@@_draw_eor_bool }
+\cs_new_protected:Npn \@@_backend_nonzero_rule:
+  { \bool_gset_false:N \g_@@_draw_eor_bool }
+\bool_new:N \g_@@_draw_eor_bool
+%    \end{macrocode}
+% \end{variable}
+% \end{macro}
+%
+% \begin{macro}
+%   {
+%     \@@_backend_closepath:   ,
+%     \@@_backend_stroke:      ,
+%     \@@_backend_closestroke: ,
+%     \@@_backend_fill:        ,
+%     \@@_backend_fillstroke:  ,
+%     \@@_backend_clip:        ,
+%     \@@_backend_discardpath:
+%   }
+%   Converting paths to output is again a case of mapping directly to
+%   PDF operations.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_closepath:
+  { \@@_backend_literal:n { h } }
+\cs_new_protected:Npn \@@_backend_stroke:
+  { \@@_backend_literal:n { S } }
+\cs_new_protected:Npn \@@_backend_closestroke:
+  { \@@_backend_literal:n { s } }
+\cs_new_protected:Npn \@@_backend_fill:
+  {
+    \@@_backend_literal:x
+      { f \bool_if:NT \g_@@_draw_eor_bool * }
+  }
+\cs_new_protected:Npn \@@_backend_fillstroke:
+  {
+    \@@_backend_literal:x
+      { B \bool_if:NT \g_@@_draw_eor_bool * }
+  }
+\cs_new_protected:Npn \@@_backend_clip:
+  {
+    \@@_backend_literal:x
+      { W \bool_if:NT \g_@@_draw_eor_bool * }
+  }
+\cs_new_protected:Npn \@@_backend_discardpath:
+  { \@@_backend_literal:n { n } }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_dash_pattern:nn}
+% \begin{macro}{\@@_backend_dash:n}
+% \begin{macro}{\@@_backend_linewidth:n}
+% \begin{macro}{\@@_backend_miterlimit:n}
+% \begin{macro}
+%   {
+%     \@@_backend_cap_butt:, \@@_backend_cap_round:, \@@_backend_cap_rectangle:,
+%     \@@_backend_join_miter:, \@@_backend_join_round:, \@@_backend_join_bevel:
+%   }
+%   Converting paths to output is again a case of mapping directly to
+%   PDF operations.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_dash_pattern:nn #1#2
+  {
+    \@@_backend_literal:x
+      {
+        [
+          \exp_args:Nf \use:n
+            { \clist_map_function:nN {#1} \@@_backend_dash:n }
+        ] ~
+        \dim_to_decimal_in_bp:n {#2} ~ d
+      }
+  }
+\cs_new:Npn \@@_backend_dash:n #1
+  { ~ \dim_to_decimal_in_bp:n {#1} }
+\cs_new_protected:Npn \@@_backend_linewidth:n #1
+  {
+    \@@_backend_literal:x
+      { \dim_to_decimal_in_bp:n {#1} ~ w }
+  }
+\cs_new_protected:Npn \@@_backend_miterlimit:n #1
+  { \@@_backend_literal:x { \fp_eval:n {#1} ~ M } }
+\cs_new_protected:Npn \@@_backend_cap_butt:
+  { \@@_backend_literal:n { 0 ~ J } }
+\cs_new_protected:Npn \@@_backend_cap_round:
+  { \@@_backend_literal:n { 1 ~ J } }
+\cs_new_protected:Npn \@@_backend_cap_rectangle:
+  { \@@_backend_literal:n { 2 ~ J } }
+\cs_new_protected:Npn \@@_backend_join_miter:
+  { \@@_backend_literal:n { 0 ~ j } }
+\cs_new_protected:Npn \@@_backend_join_round:
+  { \@@_backend_literal:n { 1 ~ j } }
+\cs_new_protected:Npn \@@_backend_join_bevel:
+  { \@@_backend_literal:n { 2 ~ j } }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}
+%   {
+%     \@@_backend_color_fill_cmyk:nnnn   ,
+%     \@@_backend_color_stroke_cmyk:nnnn
+%   }
+% \begin{macro}
+%   {
+%     \@@_backend_color_fill_gray:n   ,
+%     \@@_backend_color_stroke_gray:n
+%   }
+% \begin{macro}
+%   {
+%     \@@_backend_color_fill_rgb:nnn   ,
+%     \@@_backend_color_stroke_rgb:nnn
+%   }
+% \begin{macro}{\@@_backend_color_select:n, \@@_backend_color_select:x}
+% \begin{macro}{\@@_backend_color_reset:}
+%    Color has to be split between \texttt{(x)dvipdfmx} and the PDF engines
+%    as there is no color stack for fill/stroke separation in the former.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_color_fill_cmyk:nnnn #1#2#3#4
+  {
+    \@@_backend_color_select:x
+      {
+        \fp_eval:n {#1} ~ \fp_eval:n {#2} ~ 
+        \fp_eval:n {#3} ~ \fp_eval:n {#4} ~
+        k
+      }
+  }
+\cs_new_protected:Npn \@@_backend_color_stroke_cmyk:nnnn #1#2#3#4
+  {
+    \@@_backend_color_select:x
+      {
+        \fp_eval:n {#1} ~ \fp_eval:n {#2} ~ 
+        \fp_eval:n {#3} ~ \fp_eval:n {#4} ~
+        k
+      }
+  }
+\cs_new_protected:Npn \@@_backend_color_fill_gray:n #1
+  { \@@_backend_color_select:x { \fp_eval:n {#1} ~ g } }
+\cs_new_protected:Npn \@@_backend_color_stroke_gray:n #1
+  { \@@_backend_color_select:x { \fp_eval:n {#1} ~ G } }
+\cs_new_protected:Npn \@@_backend_color_fill_rgb:nnn #1#2#3
+  {
+    \@@_backend_color_select:x
+      { \fp_eval:n {#1} ~ \fp_eval:n {#2} ~ \fp_eval:n {#3} ~ rg }
+  }
+\cs_new_protected:Npn \@@_backend_color_stroke_rgb:nnn #1#2#3
+  {
+    \@@_backend_color_select:x
+      { \fp_eval:n {#1} ~ \fp_eval:n {#2} ~ \fp_eval:n {#3} ~ RG }
+  }
+%<*pdfmode>
+\cs_new_protected:Npx \@@_backend_color_select:n #1
+  {
+    \cs_if_exist:NTF \tex_pdfextension:D
+      { \tex_pdfextension:D colorstack }
+      { \tex_pdfcolorstack:D }
+        \exp_not:N \l__kernel_color_stack_int push {#1}
+      \group_insert_after:N \exp_not:N \@@_backend_color_reset:
+  }
+\cs_new_protected:Npx \@@_backend_color_reset:
+  {
+    \cs_if_exist:NTF \tex_pdfextension:D
+      { \tex_pdfextension:D colorstack }
+      { \tex_pdfcolorstack:D }
+        \exp_not:N \l__kernel_color_stack_int pop \scan_stop:
+  }
+%</pdfmode>
+%<*dvipdfmx|xdvipdfmx>
+\cs_new_eq:NN \@@_backend_color_select:n \__kernel_backend_literal_pdf:n
+%</dvipdfmx|xdvipdfmx>
+\cs_generate_variant:Nn \@@_backend_color_select:n { x }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_cm:nnnn}
+% \begin{macro}{\@@_backend_cm_aux:nnnn}
+%   Another split here between \texttt{pdfmode} and \texttt{(x)dvipdfmx}.
+%   In the former, we have a direct method to maintain alignment: the backend
+%   can use a matrix itself. For \texttt{(x)dvipdfmx}, we can to decompose the
+%   matrix into rotations and a scaling, then use those operations as they
+%   are handled by the backend. (There is backend support for matrix operations in
+%   \texttt{(x)dvipdfmx}, but as a matched pair so not suitable for the
+%   \enquote{stand alone} transformation set up here.)
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_cm:nnnn #1#2#3#4
+  {
+%<*pdfmode>
+    \__kernel_backend_matrix:x
+      {
+        \fp_eval:n {#1} ~ \fp_eval:n {#2} ~
+        \fp_eval:n {#3} ~ \fp_eval:n {#4}
+      }
+%</pdfmode>
+%<*dvipdfmx|xdvipdfmx>
+    \@@_backend_cm_decompose:nnnnN {#1} {#2} {#3} {#4}
+      \@@_backend_cm_aux:nnnn
+%</dvipdfmx|xdvipdfmx>
+  }
+%<*dvipdfmx|xdvipdfmx>
+\cs_new_protected:Npn \@@_backend_cm_aux:nnnn #1#2#3#4
+  {
+    \__kernel_backend_literal:x
+      {
+        x:rotate~
+        \fp_compare:nNnTF {#1} = \c_zero_fp
+          { 0 }
+          { \fp_eval:n { round ( -#1 , 5 ) } }
+      }
+    \__kernel_backend_literal:x
+      {
+        x:scale~
+        \fp_eval:n { round ( #2 , 5 ) } ~
+        \fp_eval:n { round ( #3 , 5 ) }
+      }
+    \__kernel_backend_literal:x
+      {
+        x:rotate~
+        \fp_compare:nNnTF {#4} = \c_zero_fp
+          { 0 }
+          { \fp_eval:n { round ( -#4 , 5 ) } }
+      }
+  }
+%</dvipdfmx|xdvipdfmx>
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_cm_decompose:nnnnN}
+% \begin{macro}
+%   {
+%     \@@_backend_cm_decompose_auxi:nnnnN,
+%     \@@_backend_cm_decompose_auxii:nnnnN,
+%     \@@_backend_cm_decompose_auxiii:nnnnN,
+%   }
+%   Internally, transformations for drawing are tracked as a matrix. Not all
+%   engines provide a way of dealing with this: if we use a raw matrix, the
+%   engine looses track of positions (for example for hyperlinks), and this is
+%   not desirable. They do, however, allow us to track rotations and scalings.
+%   Luckily, we can decompose any (two-dimensional) matrix into two rotations
+%   and a single scaling:
+%   \[
+%     \begin{bmatrix}
+%         A & B \\ C & D
+%     \end{bmatrix}
+%     =
+%     \begin{bmatrix}
+%       \cos\beta & \sin\beta \\ -\sin\beta & \cos\beta
+%     \end{bmatrix}
+%     \begin{bmatrix}
+%       w_{1} & 0 \\ 0 & w_{2}
+%     \end{bmatrix}
+%     \begin{bmatrix}
+%       \cos\gamma & \sin\gamma \\ -\sin\gamma & \cos\gamma
+%     \end{bmatrix} 
+%   \]
+%   The parent matrix can be converted to
+%   \[
+%     \begin{bmatrix}
+%       A & B \\ C & D
+%     \end{bmatrix}
+%      =
+%     \begin{bmatrix}
+%       E & H \\-H & E
+%     \end{bmatrix}
+%     +
+%     \begin{bmatrix}
+%       F & G \\ G & -F
+%     \end{bmatrix}
+%   \]
+%   From these, we can find that
+%   \begin{align*}
+%     \frac{w_{1} + w_{2}}{2} &= \sqrt{E^{2} + H^{2}} \\
+%     \frac{w_{1} - w_{2}}{2} &= \sqrt{F^{2} + G^{2}} \\
+%     \gamma - \beta &= \tan^{-1}(G/F) \\
+%     \gamma + \beta &= \tan^{-1}(H/E)
+%   \end{align*}
+%   at which point we just have to do various pieces of re-arrangement to
+%   get all of the values. (See J.~Blinn, \emph{IEEE Comput.\ Graph.\ Appl.},
+%   1996, \textbf{16}, 82--88.) There is one wrinkle: the PostScript (and PDF)
+%   way of specifying a transformation matrix exchanges where one would
+%   normally expect $B$ and $C$ to be.
+%    \begin{macrocode}
+%<*dvipdfmx|xdvipdfmx>
+\cs_new_protected:Npn \@@_backend_cm_decompose:nnnnN #1#2#3#4#5
+  {
+    \use:x
+      {
+        \@@_backend_cm_decompose_auxi:nnnnN
+          { \fp_eval:n { (#1 + #4) / 2 } }
+          { \fp_eval:n { (#1 - #4) / 2 } }
+          { \fp_eval:n { (#3 + #2) / 2 } }
+          { \fp_eval:n { (#3 - #2) / 2 } }
+      }
+        #5
+  }
+\cs_new_protected:Npn \@@_backend_cm_decompose_auxi:nnnnN #1#2#3#4#5
+  {
+    \use:x
+      {
+        \@@_backend_cm_decompose_auxii:nnnnN
+          { \fp_eval:n { 2 * sqrt ( #1 * #1 + #4 * #4 ) } }
+          { \fp_eval:n { 2 * sqrt ( #2 * #2 + #3 * #3 ) } }
+          { \fp_eval:n { atand ( #3 , #2 ) } }
+          { \fp_eval:n { atand ( #4 , #1 ) } }
+      }
+         #5
+  }
+\cs_new_protected:Npn \@@_backend_cm_decompose_auxii:nnnnN #1#2#3#4#5
+  {
+    \use:x
+      {
+        \@@_backend_cm_decompose_auxiii:nnnnN
+          { \fp_eval:n { ( #4 - #3 ) / 2 } }
+          { \fp_eval:n { ( #1 + #2 ) / 2 } }
+          { \fp_eval:n { ( #1 - #2 ) / 2 } }
+          { \fp_eval:n { ( #4 + #3 ) / 2 } }
+      }
+        #5
+  }
+\cs_new_protected:Npn \@@_backend_cm_decompose_auxiii:nnnnN #1#2#3#4#5
+  {
+    \fp_compare:nNnTF { abs( #2 ) } > { abs ( #3 ) }
+      { #5 {#1} {#2} {#3} {#4} }
+      { #5 {#1} {#3} {#2} {#4} }
+  }
+%</dvipdfmx|xdvipdfmx>
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_box_use:Nnnnn}
+%   Inserting a \TeX{} box transformed to the requested position and using
+%   the current matrix is done using a mixture of \TeX{} and low-level
+%   manipulation. The offset can be handled by \TeX{}, so only any rotation/^^A
+%   skew/scaling component needs to be done using the matrix operation. As this
+%   operation can never be cached, the scope is set directly not using the
+%   \texttt{draw} version.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_box_use:Nnnnn #1#2#3#4#5
+  {
+    \__kernel_backend_scope_begin:
+%<*pdfmode>
+    \@@_backend_cm:nnnn {#2} {#3} {#4} {#5}
+%</pdfmode>
+%<*dvipdfmx|xdvipdfmx>
+    \__kernel_backend_literal:x
+      {
+        pdf:btrans~matrix~
+        \fp_eval:n {#2} ~ \fp_eval:n {#3} ~
+        \fp_eval:n {#4} ~ \fp_eval:n {#5} ~
+        0 ~ 0
+      }
+%</dvipdfmx|xdvipdfmx>
+    \hbox_overlap_right:n { \box_use:N #1 }
+%<*dvipdfmx|xdvipdfmx>
+    \__kernel_backend_literal:n { pdf:etrans }
+%</dvipdfmx|xdvipdfmx>
+    \__kernel_backend_scope_end:
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%    \begin{macrocode}
+%</dvipdfmx|pdfmode|xdvipdfmx>
+%    \end{macrocode}
+%
+% \subsection{\texttt{dvisvgm} backend}
+%
+%    \begin{macrocode}
+%<*dvisvgm>
+%    \end{macrocode}
+%
+% \begin{macro}{\@@_backend_literal:n, \@@_backend_literal:x}
+%   The same as the more general literal call.
+%    \begin{macrocode}
+\cs_new_eq:NN \@@_backend_literal:n \__kernel_backend_literal_svg:n
+\cs_generate_variant:Nn \@@_backend_literal:n { x }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_begin:, \@@_backend_end:}
+%   A drawing needs to be set up such that the co-ordinate system is
+%   translated. That is done inside a scope, which as described below
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_begin:
+  {
+    \@@_backend_scope_begin:
+    \@@_backend_scope:n { transform="translate({?x},{?y})~scale(1,-1)" }
+  }
+\cs_new_protected:Npn \@@_backend_end:
+  { \@@_backend_scope_end: }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_scope_begin:, \@@_backend_scope_end:}
+% \begin{macro}{\@@_backend_scope:n, \@@_backend_scope:x}
+% \begin{variable}{\g_@@_draw_scope_int, \l_@@_draw_scope_int}
+%   Several settings that with other backends are \enquote{stand alone} have
+%   to be given as part of a scope in SVG. As a result, there is a need to
+%   provide a mechanism to automatically close these extra scopes. That is
+%   done using a dedicated function and a pair of tracking variables. Within
+%   each graphics scope we use a global variable to do the work, with a group
+%   used to save the value between scopes. The result is that no direct action
+%   is needed when creating a scope.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_scope_begin:
+  {
+    \int_set_eq:NN
+      \l_@@_draw_scope_int
+      \g_@@_draw_scope_int
+    \group_begin:
+      \int_gzero:N \g_@@_draw_scope_int
+  }
+\cs_new_protected:Npn \@@_backend_scope_end:
+  {
+      \prg_replicate:nn
+        { \g_@@_draw_scope_int }
+        { \@@_backend_literal:n { </g> } }
+    \group_end:
+    \int_gset_eq:NN
+      \g_@@_draw_scope_int
+      \l_@@_draw_scope_int
+  }
+\cs_new_protected:Npn \@@_backend_scope:n #1
+  {
+    \@@_backend_literal:n { <g~ #1 > }
+    \int_gincr:N \g_@@_draw_scope_int
+  }
+\cs_generate_variant:Nn \@@_backend_scope:n { x }
+\int_new:N \g_@@_draw_scope_int
+\int_new:N \l_@@_draw_scope_int
+%    \end{macrocode}
+% \end{variable}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_moveto:nn, \@@_backend_lineto:nn}
+% \begin{macro}{\@@_backend_rectangle:nnnn}
+% \begin{macro}{\@@_backend_curveto:nnnnnn}
+% \begin{macro}{\@@_backend_add_to_path:n}
+% \begin{variable}{\g_@@_draw_path_tl}
+%   Once again, some work is needed to get path constructs correct. Rather
+%   then write the values as they are given, the entire path needs to be
+%   collected up before being output in one go. For that we use a dedicated
+%   storage routine, which adds spaces as required. Since paths should
+%   be fully expanded there is no need to worry about the internal
+%   \texttt{x}-type expansion.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_moveto:nn #1#2
+  {
+    \@@_backend_add_to_path:n
+      { M ~ \dim_to_decimal:n {#1} ~ \dim_to_decimal:n {#2} }
+  }
+\cs_new_protected:Npn \@@_backend_lineto:nn #1#2
+  {
+    \@@_backend_add_to_path:n
+      { L ~ \dim_to_decimal:n {#1} ~ \dim_to_decimal:n {#2} }
+  }
+\cs_new_protected:Npn \@@_backend_rectangle:nnnn #1#2#3#4
+  {
+    \@@_backend_add_to_path:n
+      {
+        M ~ \dim_to_decimal:n {#1} ~ \dim_to_decimal:n {#2}
+        h ~ \dim_to_decimal:n {#3} ~
+        v ~ \dim_to_decimal:n {#4} ~
+        h ~ \dim_to_decimal:n { -#3 } ~
+        Z
+      }
+  }
+\cs_new_protected:Npn \@@_backend_curveto:nnnnnn #1#2#3#4#5#6
+  {
+    \@@_backend_add_to_path:n
+      {
+        C ~
+        \dim_to_decimal:n {#1} ~ \dim_to_decimal:n {#2} ~
+        \dim_to_decimal:n {#3} ~ \dim_to_decimal:n {#4} ~
+        \dim_to_decimal:n {#5} ~ \dim_to_decimal:n {#6}
+      }
+  }
+\cs_new_protected:Npn \@@_backend_add_to_path:n #1
+  {
+    \tl_gset:Nx \g_@@_draw_path_tl
+      {
+        \g_@@_draw_path_tl
+        \tl_if_empty:NF \g_@@_draw_path_tl { \c_space_tl }
+        #1
+      }
+  }
+\tl_new:N \g_@@_draw_path_tl
+%    \end{macrocode}
+% \end{variable}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_evenodd_rule:, \@@_backend_nonzero_rule:}
+%   The fill rules here have to be handled as scopes.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_evenodd_rule:
+  { \@@_backend_scope:n { fill-rule="evenodd" } }
+\cs_new_protected:Npn \@@_backend_nonzero_rule:
+  { \@@_backend_scope:n { fill-rule="nonzero" } }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_path:n}
+% \begin{macro}
+%   {
+%     \@@_backend_closepath:   ,
+%     \@@_backend_stroke:      ,
+%     \@@_backend_closestroke: ,
+%     \@@_backend_fill:        ,
+%     \@@_backend_fillstroke:  ,
+%     \@@_backend_clip:        ,
+%     \@@_backend_discardpath:
+%   }
+% \begin{variable}{\g_@@_draw_clip_bool}
+% \begin{variable}{\g_@@_draw_path_int}
+%   Setting fill and stroke effects and doing clipping all has to be done using
+%   scopes. This means setting up the various requirements in a shared
+%   auxiliary which deals with the bits and pieces. Clipping paths are reused
+%   for path drawing: not essential but avoids constructing them twice.
+%   Discarding a path needs a separate function as it's not quite the same.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_closepath:
+  { \@@_backend_add_to_path:n { Z } }
+\cs_new_protected:Npn \@@_backend_path:n #1
+  {
+    \bool_if:NTF \g_@@_draw_clip_bool
+      {
+        \int_gincr:N \g_@@_clip_path_int
+        \@@_backend_literal:x
+          {
+            < clipPath~id = " l3cp \int_use:N \g_@@_clip_path_int " >
+              { ?nl }
+            <path~d=" \g_@@_draw_path_tl "/> { ?nl }
+            < /clipPath > { ? nl }
+            <
+              use~xlink:href =
+                "\c_hash_str l3path \int_use:N \g_@@_path_int " ~
+                #1
+            />
+          }
+        \@@_backend_scope:x
+          {
+            clip-path =
+              "url( \c_hash_str l3cp \int_use:N \g_@@_clip_path_int)"
+          }
+      }
+      {
+        \@@_backend_literal:x
+          { <path ~ d=" \g_@@_draw_path_tl " ~ #1 /> }
+      }
+    \tl_gclear:N \g_@@_draw_path_tl
+    \bool_gset_false:N \g_@@_draw_clip_bool
+  }
+\int_new:N \g_@@_path_int
+\cs_new_protected:Npn \@@_backend_stroke:
+  { \@@_backend_path:n { style="fill:none" } }
+\cs_new_protected:Npn \@@_backend_closestroke:
+  {
+    \@@_backend_closepath:
+    \@@_backend_stroke:
+  }
+\cs_new_protected:Npn \@@_backend_fill:
+  { \@@_backend_path:n { style="stroke:none" } }
+\cs_new_protected:Npn \@@_backend_fillstroke:
+  { \@@_backend_path:n { } }
+\cs_new_protected:Npn \@@_backend_clip:
+  { \bool_gset_true:N \g_@@_draw_clip_bool }
+\bool_new:N \g_@@_draw_clip_bool
+\cs_new_protected:Npn \@@_backend_discardpath:
+  {
+    \bool_if:NT \g_@@_draw_clip_bool
+      {
+        \int_gincr:N \g_@@_clip_path_int
+        \@@_backend_literal:x
+          {
+            < clipPath~id = " l3cp \int_use:N \g_@@_clip_path_int " >
+              { ?nl }
+            <path~d=" \g_@@_draw_path_tl "/> { ?nl }
+            < /clipPath >
+          }
+        \@@_backend_scope:x
+          {
+            clip-path =
+              "url( \c_hash_str l3cp \int_use:N \g_@@_clip_path_int)"
+          }
+      }
+    \tl_gclear:N \g_@@_draw_path_tl
+    \bool_gset_false:N \g_@@_draw_clip_bool
+  }
+%    \end{macrocode}
+% \end{variable}
+% \end{variable}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_dash_pattern:nn}
+% \begin{macro}{\@@_backend_dash:n}
+% \begin{macro}{\@@_backend_dash_aux:nn}
+% \begin{macro}{\@@_backend_linewidth:n}
+% \begin{macro}{\@@_backend_miterlimit:n}
+% \begin{macro}
+%   {
+%     \@@_backend_cap_butt:, \@@_backend_cap_round:, \@@_backend_cap_rectangle:,
+%     \@@_backend_join_miter:, \@@_backend_join_round:, \@@_backend_join_bevel:
+%   }
+%   All of these ideas are properties of scopes in SVG. The only slight
+%   complexity is converting the dash array properly (doing any required
+%   maths).
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_dash_pattern:nn #1#2
+  {
+    \use:x
+      {
+        \@@_backend_dash_aux:nn
+          { \clist_map_function:nn {#1} \@@_backend_dash:n }
+          { \dim_to_decimal:n {#2} }
+      }
+  }
+\cs_new:Npn \@@_backend_dash:n #1
+  { , \dim_to_decimal_in_bp:n {#1} }
+\cs_new_protected:Npn \@@_backend_dash_aux:nn #1#2
+  {
+    \@@_backend_scope:x
+      {
+        stroke-dasharray =
+          "
+            \tl_if_empty:oTF { \use_none:n #1 }
+              { none }
+              { \use_none:n #1 }
+          " ~
+          stroke-offset=" #2 "
+      }
+  }
+\cs_new_protected:Npn \@@_backend_linewidth:n #1
+  { \@@_backend_scope:x { stroke-width=" \dim_to_decimal:n {#1} " } }
+\cs_new_protected:Npn \@@_backend_miterlimit:n #1
+  { \@@_backend_scope:x { stroke-miterlimit=" \fp_eval:n {#1} " } }
+\cs_new_protected:Npn \@@_backend_cap_butt:
+  { \@@_backend_scope:n { stroke-linecap="butt" } }
+\cs_new_protected:Npn \@@_backend_cap_round:
+  { \@@_backend_scope:n { stroke-linecap="round" } }
+\cs_new_protected:Npn \@@_backend_cap_rectangle:
+  { \@@_backend_scope:n { stroke-linecap="square" } }
+\cs_new_protected:Npn \@@_backend_join_miter:
+  { \@@_backend_scope:n { stroke-linejoin="miter" } }
+\cs_new_protected:Npn \@@_backend_join_round:
+  { \@@_backend_scope:n { stroke-linejoin="round" } }
+\cs_new_protected:Npn \@@_backend_join_bevel:
+  { \@@_backend_scope:n { stroke-linejoin="bevel" } }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}
+%   {
+%     \@@_backend_color_fill_cmyk:nnnn   ,
+%     \@@_backend_color_stroke_cmyk:nnnn
+%   }
+% \begin{macro}
+%   {
+%     \@@_backend_color_fill_gray:n   ,
+%     \@@_backend_color_stroke_gray:n
+%   }
+% \begin{macro}
+%   {
+%     \@@_backend_color_fill_rgb:nnn   ,
+%     \@@_backend_color_stroke_rgb:nnn
+%   }
+% \begin{macro}{\@@_backend_color_fill:nnn}
+%  SVG fill color has to be covered outside of the stack, as for
+%  \texttt{dvips}. Here, we are only allowed RGB colors so there is some
+%  conversion to do.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_color_fill_cmyk:nnnn #1#2#3#4
+  {
+    \use:x
+      {
+        \@@_backend_color_fill:nnn
+          { \fp_eval:n { -100 * ( (#1) * ( 1 - (#4) ) - 1 ) } }
+          { \fp_eval:n { -100 * ( (#2) * ( 1 - (#4) ) + #4 - 1 ) } }
+          { \fp_eval:n { -100 * ( (#3) * ( 1 - (#4) ) + #4 - 1 ) } }
+      }
+  }
+\cs_new_protected:Npn \@@_backend_color_stroke_cmyk:nnnn #1#2#3#4
+  {
+    \@@_backend_select:x
+      {
+        cmyk~
+        \fp_eval:n {#1} ~ \fp_eval:n {#2} ~
+        \fp_eval:n {#3} ~ \fp_eval:n {#4}
+      }
+  }
+\cs_new_protected:Npn \@@_backend_color_fill_gray:n #1
+  {
+    \use:x
+      {
+        \@@_backend_color_gray_aux:n
+          { \fp_eval:n { 100 * (#1) } }
+      }
+  }
+\cs_new_protected:Npn \@@_backend_color_gray_aux:n #1
+  { \@@_backend_color_fill:nnn {#1} {#1} {#1} }
+\cs_new_protected:Npn \@@_backend_color_stroke_gray:n #1
+  { \@@_backend_select:x { gray~ \fp_eval:n {#1} } }
+\cs_new_protected:Npn \@@_backend_color_fill_rgb:nnn #1#2#3
+  {
+    \use:x
+      {
+        \@@_backend_color_fill:nnn
+          { \fp_eval:n { 100 * (#1) } }
+          { \fp_eval:n { 100 * (#2) } }
+          { \fp_eval:n { 100 * (#3) } }
+      }
+  }
+\cs_new_protected:Npn \@@_backend_color_fill:nnn #1#2#3
+  {
+    \@@_backend_scope:x
+      {
+        fill =
+         "
+           rgb
+             (
+               #1 \c_percent_str ,
+               #2 \c_percent_str ,
+               #3 \c_percent_str
+             )
+         "
+      }
+  }
+\cs_new_protected:Npn \@@_backend_color_stroke_rgb:nnn #1#2#3
+  {
+    \@@_backend_select:x
+      { rgb~ \fp_eval:n {#1} ~ \fp_eval:n {#2} ~ \fp_eval:n {#3} }
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_cm:nnnn}
+%   The four arguments here are floats (the affine matrix), the last
+%   two are a displacement vector. 
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_cm:nnnn #1#2#3#4
+  {
+    \@@_backend_scope:n
+      {
+       transform =
+         "
+           matrix
+             (
+               \fp_eval:n {#1} , \fp_eval:n {#2} ,
+               \fp_eval:n {#3} , \fp_eval:n {#4} ,
+               0pt , 0pt
+             )
+         "
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_backend_box_use:Nnnnn}
+%   No special savings can be made here: simply displace the box inside
+%   a scope. As there is nothing to re-box, just make the box passed of
+%   zero size.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_backend_box_use:Nnnnn #1#2#3#4#5#6#7
+  {
+    \__kernel_backend_scope_begin:
+    \@@_backend_cm:nnnn {#2} {#3} {#4} {#5}
+    \__kernel_backend_literal_svg:n
+      {
+        < g~
+            stroke="none"~
+            transform="scale(-1,1)~translate({?x},{?y})~scale(-1,-1)"
+        >
+      }
+    \box_set_wd:Nn #1 { 0pt }
+    \box_set_ht:Nn #1 { 0pt }
+    \box_set_dp:Nn #1 { 0pt }
+    \box_use:N #1
+    \__kernel_backend_literal_svg:n { </g> }
+    \__kernel_backend_scope_end:
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%    \begin{macrocode}
+%</dvisvgm>
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+%</initex|package>
+%    \end{macrocode}
+%
+% \end{implementation}
+%
+% \PrintIndex