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-=encoding utf8
-
-=head1 NAME
-
-perlpodspec - Plain Old Documentation: format specification and notes
-
-=head1 DESCRIPTION
-
-This document is detailed notes on the Pod markup language. Most
-people will only have to read L<perlpod|perlpod> to know how to write
-in Pod, but this document may answer some incidental questions to do
-with parsing and rendering Pod.
-
-In this document, "must" / "must not", "should" /
-"should not", and "may" have their conventional (cf. RFC 2119)
-meanings: "X must do Y" means that if X doesn't do Y, it's against
-this specification, and should really be fixed. "X should do Y"
-means that it's recommended, but X may fail to do Y, if there's a
-good reason. "X may do Y" is merely a note that X can do Y at
-will (although it is up to the reader to detect any connotation of
-"and I think it would be I<nice> if X did Y" versus "it wouldn't
-really I<bother> me if X did Y").
-
-Notably, when I say "the parser should do Y", the
-parser may fail to do Y, if the calling application explicitly
-requests that the parser I<not> do Y. I often phrase this as
-"the parser should, by default, do Y." This doesn't I<require>
-the parser to provide an option for turning off whatever
-feature Y is (like expanding tabs in verbatim paragraphs), although
-it implicates that such an option I<may> be provided.
-
-=head1 Pod Definitions
-
-Pod is embedded in files, typically Perl source files, although you
-can write a file that's nothing but Pod.
-
-A B<line> in a file consists of zero or more non-newline characters,
-terminated by either a newline or the end of the file.
-
-A B<newline sequence> is usually a platform-dependent concept, but
-Pod parsers should understand it to mean any of CR (ASCII 13), LF
-(ASCII 10), or a CRLF (ASCII 13 followed immediately by ASCII 10), in
-addition to any other system-specific meaning. The first CR/CRLF/LF
-sequence in the file may be used as the basis for identifying the
-newline sequence for parsing the rest of the file.
-
-A B<blank line> is a line consisting entirely of zero or more spaces
-(ASCII 32) or tabs (ASCII 9), and terminated by a newline or end-of-file.
-A B<non-blank line> is a line containing one or more characters other
-than space or tab (and terminated by a newline or end-of-file).
-
-(I<Note:> Many older Pod parsers did not accept a line consisting of
-spaces/tabs and then a newline as a blank line. The only lines they
-considered blank were lines consisting of I<no characters at all>,
-terminated by a newline.)
-
-B<Whitespace> is used in this document as a blanket term for spaces,
-tabs, and newline sequences. (By itself, this term usually refers
-to literal whitespace. That is, sequences of whitespace characters
-in Pod source, as opposed to "EE<lt>32>", which is a formatting
-code that I<denotes> a whitespace character.)
-
-A B<Pod parser> is a module meant for parsing Pod (regardless of
-whether this involves calling callbacks or building a parse tree or
-directly formatting it). A B<Pod formatter> (or B<Pod translator>)
-is a module or program that converts Pod to some other format (HTML,
-plaintext, TeX, PostScript, RTF). A B<Pod processor> might be a
-formatter or translator, or might be a program that does something
-else with the Pod (like counting words, scanning for index points,
-etc.).
-
-Pod content is contained in B<Pod blocks>. A Pod block starts with a
-line that matches <m/\A=[a-zA-Z]/>, and continues up to the next line
-that matches C<m/\A=cut/> or up to the end of the file if there is
-no C<m/\A=cut/> line.
-
-=for comment
- The current perlsyn says:
- [beginquote]
- Note that pod translators should look at only paragraphs beginning
- with a pod directive (it makes parsing easier), whereas the compiler
- actually knows to look for pod escapes even in the middle of a
- paragraph. This means that the following secret stuff will be ignored
- by both the compiler and the translators.
- $a=3;
- =secret stuff
- warn "Neither POD nor CODE!?"
- =cut back
- print "got $a\n";
- You probably shouldn't rely upon the warn() being podded out forever.
- Not all pod translators are well-behaved in this regard, and perhaps
- the compiler will become pickier.
- [endquote]
- I think that those paragraphs should just be removed; paragraph-based
- parsing seems to have been largely abandoned, because of the hassle
- with non-empty blank lines messing up what people meant by "paragraph".
- Even if the "it makes parsing easier" bit were especially true,
- it wouldn't be worth the confusion of having perl and pod2whatever
- actually disagree on what can constitute a Pod block.
-
-Within a Pod block, there are B<Pod paragraphs>. A Pod paragraph
-consists of non-blank lines of text, separated by one or more blank
-lines.
-
-For purposes of Pod processing, there are four types of paragraphs in
-a Pod block:
-
-=over
-
-=item *
-
-A command paragraph (also called a "directive"). The first line of
-this paragraph must match C<m/\A=[a-zA-Z]/>. Command paragraphs are
-typically one line, as in:
-
- =head1 NOTES
-
- =item *
-
-But they may span several (non-blank) lines:
-
- =for comment
- Hm, I wonder what it would look like if
- you tried to write a BNF for Pod from this.
-
- =head3 Dr. Strangelove, or: How I Learned to
- Stop Worrying and Love the Bomb
-
-I<Some> command paragraphs allow formatting codes in their content
-(i.e., after the part that matches C<m/\A=[a-zA-Z]\S*\s*/>), as in:
-
- =head1 Did You Remember to C<use strict;>?
-
-In other words, the Pod processing handler for "head1" will apply the
-same processing to "Did You Remember to CE<lt>use strict;>?" that it
-would to an ordinary paragraph (i.e., formatting codes like
-"CE<lt>...>") are parsed and presumably formatted appropriately, and
-whitespace in the form of literal spaces and/or tabs is not
-significant.
-
-=item *
-
-A B<verbatim paragraph>. The first line of this paragraph must be a
-literal space or tab, and this paragraph must not be inside a "=begin
-I<identifier>", ... "=end I<identifier>" sequence unless
-"I<identifier>" begins with a colon (":"). That is, if a paragraph
-starts with a literal space or tab, but I<is> inside a
-"=begin I<identifier>", ... "=end I<identifier>" region, then it's
-a data paragraph, unless "I<identifier>" begins with a colon.
-
-Whitespace I<is> significant in verbatim paragraphs (although, in
-processing, tabs are probably expanded).
-
-=item *
-
-An B<ordinary paragraph>. A paragraph is an ordinary paragraph
-if its first line matches neither C<m/\A=[a-zA-Z]/> nor
-C<m/\A[ \t]/>, I<and> if it's not inside a "=begin I<identifier>",
-... "=end I<identifier>" sequence unless "I<identifier>" begins with
-a colon (":").
-
-=item *
-
-A B<data paragraph>. This is a paragraph that I<is> inside a "=begin
-I<identifier>" ... "=end I<identifier>" sequence where
-"I<identifier>" does I<not> begin with a literal colon (":"). In
-some sense, a data paragraph is not part of Pod at all (i.e.,
-effectively it's "out-of-band"), since it's not subject to most kinds
-of Pod parsing; but it is specified here, since Pod
-parsers need to be able to call an event for it, or store it in some
-form in a parse tree, or at least just parse I<around> it.
-
-=back
-
-For example: consider the following paragraphs:
-
- # <- that's the 0th column
-
- =head1 Foo
-
- Stuff
-
- $foo->bar
-
- =cut
-
-Here, "=head1 Foo" and "=cut" are command paragraphs because the first
-line of each matches C<m/\A=[a-zA-Z]/>. "I<[space][space]>$foo->bar"
-is a verbatim paragraph, because its first line starts with a literal
-whitespace character (and there's no "=begin"..."=end" region around).
-
-The "=begin I<identifier>" ... "=end I<identifier>" commands stop
-paragraphs that they surround from being parsed as ordinary or verbatim
-paragraphs, if I<identifier> doesn't begin with a colon. This
-is discussed in detail in the section
-L</About Data Paragraphs and "=beginE<sol>=end" Regions>.
-
-=head1 Pod Commands
-
-This section is intended to supplement and clarify the discussion in
-L<perlpod/"Command Paragraph">. These are the currently recognized
-Pod commands:
-
-=over
-
-=item "=head1", "=head2", "=head3", "=head4"
-
-This command indicates that the text in the remainder of the paragraph
-is a heading. That text may contain formatting codes. Examples:
-
- =head1 Object Attributes
-
- =head3 What B<Not> to Do!
-
-=item "=pod"
-
-This command indicates that this paragraph begins a Pod block. (If we
-are already in the middle of a Pod block, this command has no effect at
-all.) If there is any text in this command paragraph after "=pod",
-it must be ignored. Examples:
-
- =pod
-
- This is a plain Pod paragraph.
-
- =pod This text is ignored.
-
-=item "=cut"
-
-This command indicates that this line is the end of this previously
-started Pod block. If there is any text after "=cut" on the line, it must be
-ignored. Examples:
-
- =cut
-
- =cut The documentation ends here.
-
- =cut
- # This is the first line of program text.
- sub foo { # This is the second.
-
-It is an error to try to I<start> a Pod block with a "=cut" command. In
-that case, the Pod processor must halt parsing of the input file, and
-must by default emit a warning.
-
-=item "=over"
-
-This command indicates that this is the start of a list/indent
-region. If there is any text following the "=over", it must consist
-of only a nonzero positive numeral. The semantics of this numeral is
-explained in the L</"About =over...=back Regions"> section, further
-below. Formatting codes are not expanded. Examples:
-
- =over 3
-
- =over 3.5
-
- =over
-
-=item "=item"
-
-This command indicates that an item in a list begins here. Formatting
-codes are processed. The semantics of the (optional) text in the
-remainder of this paragraph are
-explained in the L</"About =over...=back Regions"> section, further
-below. Examples:
-
- =item
-
- =item *
-
- =item *
-
- =item 14
-
- =item 3.
-
- =item C<< $thing->stuff(I<dodad>) >>
-
- =item For transporting us beyond seas to be tried for pretended
- offenses
-
- =item He is at this time transporting large armies of foreign
- mercenaries to complete the works of death, desolation and
- tyranny, already begun with circumstances of cruelty and perfidy
- scarcely paralleled in the most barbarous ages, and totally
- unworthy the head of a civilized nation.
-
-=item "=back"
-
-This command indicates that this is the end of the region begun
-by the most recent "=over" command. It permits no text after the
-"=back" command.
-
-=item "=begin formatname"
-
-=item "=begin formatname parameter"
-
-This marks the following paragraphs (until the matching "=end
-formatname") as being for some special kind of processing. Unless
-"formatname" begins with a colon, the contained non-command
-paragraphs are data paragraphs. But if "formatname" I<does> begin
-with a colon, then non-command paragraphs are ordinary paragraphs
-or data paragraphs. This is discussed in detail in the section
-L</About Data Paragraphs and "=beginE<sol>=end" Regions>.
-
-It is advised that formatnames match the regexp
-C<m/\A:?[-a-zA-Z0-9_]+\z/>. Everything following whitespace after the
-formatname is a parameter that may be used by the formatter when dealing
-with this region. This parameter must not be repeated in the "=end"
-paragraph. Implementors should anticipate future expansion in the
-semantics and syntax of the first parameter to "=begin"/"=end"/"=for".
-
-=item "=end formatname"
-
-This marks the end of the region opened by the matching
-"=begin formatname" region. If "formatname" is not the formatname
-of the most recent open "=begin formatname" region, then this
-is an error, and must generate an error message. This
-is discussed in detail in the section
-L</About Data Paragraphs and "=beginE<sol>=end" Regions>.
-
-=item "=for formatname text..."
-
-This is synonymous with:
-
- =begin formatname
-
- text...
-
- =end formatname
-
-That is, it creates a region consisting of a single paragraph; that
-paragraph is to be treated as a normal paragraph if "formatname"
-begins with a ":"; if "formatname" I<doesn't> begin with a colon,
-then "text..." will constitute a data paragraph. There is no way
-to use "=for formatname text..." to express "text..." as a verbatim
-paragraph.
-
-=item "=encoding encodingname"
-
-This command, which should occur early in the document (at least
-before any non-US-ASCII data!), declares that this document is
-encoded in the encoding I<encodingname>, which must be
-an encoding name that L<Encode> recognizes. (Encode's list
-of supported encodings, in L<Encode::Supported>, is useful here.)
-If the Pod parser cannot decode the declared encoding, it
-should emit a warning and may abort parsing the document
-altogether.
-
-A document having more than one "=encoding" line should be
-considered an error. Pod processors may silently tolerate this if
-the not-first "=encoding" lines are just duplicates of the
-first one (e.g., if there's a "=encoding utf8" line, and later on
-another "=encoding utf8" line). But Pod processors should complain if
-there are contradictory "=encoding" lines in the same document
-(e.g., if there is a "=encoding utf8" early in the document and
-"=encoding big5" later). Pod processors that recognize BOMs
-may also complain if they see an "=encoding" line
-that contradicts the BOM (e.g., if a document with a UTF-16LE
-BOM has an "=encoding shiftjis" line).
-
-=back
-
-If a Pod processor sees any command other than the ones listed
-above (like "=head", or "=haed1", or "=stuff", or "=cuttlefish",
-or "=w123"), that processor must by default treat this as an
-error. It must not process the paragraph beginning with that
-command, must by default warn of this as an error, and may
-abort the parse. A Pod parser may allow a way for particular
-applications to add to the above list of known commands, and to
-stipulate, for each additional command, whether formatting
-codes should be processed.
-
-Future versions of this specification may add additional
-commands.
-
-
-
-=head1 Pod Formatting Codes
-
-(Note that in previous drafts of this document and of perlpod,
-formatting codes were referred to as "interior sequences", and
-this term may still be found in the documentation for Pod parsers,
-and in error messages from Pod processors.)
-
-There are two syntaxes for formatting codes:
-
-=over
-
-=item *
-
-A formatting code starts with a capital letter (just US-ASCII [A-Z])
-followed by a "<", any number of characters, and ending with the first
-matching ">". Examples:
-
- That's what I<you> think!
-
- What's C<dump()> for?
-
- X<C<chmod> and C<unlink()> Under Different Operating Systems>
-
-=item *
-
-A formatting code starts with a capital letter (just US-ASCII [A-Z])
-followed by two or more "<"'s, one or more whitespace characters,
-any number of characters, one or more whitespace characters,
-and ending with the first matching sequence of two or more ">"'s, where
-the number of ">"'s equals the number of "<"'s in the opening of this
-formatting code. Examples:
-
- That's what I<< you >> think!
-
- C<<< open(X, ">>thing.dat") || die $! >>>
-
- B<< $foo->bar(); >>
-
-With this syntax, the whitespace character(s) after the "CE<lt><<"
-and before the ">>" (or whatever letter) are I<not> renderable. They
-do not signify whitespace, are merely part of the formatting codes
-themselves. That is, these are all synonymous:
-
- C<thing>
- C<< thing >>
- C<< thing >>
- C<<< thing >>>
- C<<<<
- thing
- >>>>
-
-and so on.
-
-Finally, the multiple-angle-bracket form does I<not> alter the interpretation
-of nested formatting codes, meaning that the following four example lines are
-identical in meaning:
-
- B<example: C<$a E<lt>=E<gt> $b>>
-
- B<example: C<< $a <=> $b >>>
-
- B<example: C<< $a E<lt>=E<gt> $b >>>
-
- B<<< example: C<< $a E<lt>=E<gt> $b >> >>>
-
-=back
-
-In parsing Pod, a notably tricky part is the correct parsing of
-(potentially nested!) formatting codes. Implementors should
-consult the code in the C<parse_text> routine in Pod::Parser as an
-example of a correct implementation.
-
-=over
-
-=item C<IE<lt>textE<gt>> -- italic text
-
-See the brief discussion in L<perlpod/"Formatting Codes">.
-
-=item C<BE<lt>textE<gt>> -- bold text
-
-See the brief discussion in L<perlpod/"Formatting Codes">.
-
-=item C<CE<lt>codeE<gt>> -- code text
-
-See the brief discussion in L<perlpod/"Formatting Codes">.
-
-=item C<FE<lt>filenameE<gt>> -- style for filenames
-
-See the brief discussion in L<perlpod/"Formatting Codes">.
-
-=item C<XE<lt>topic nameE<gt>> -- an index entry
-
-See the brief discussion in L<perlpod/"Formatting Codes">.
-
-This code is unusual in that most formatters completely discard
-this code and its content. Other formatters will render it with
-invisible codes that can be used in building an index of
-the current document.
-
-=item C<ZE<lt>E<gt>> -- a null (zero-effect) formatting code
-
-Discussed briefly in L<perlpod/"Formatting Codes">.
-
-This code is unusual is that it should have no content. That is,
-a processor may complain if it sees C<ZE<lt>potatoesE<gt>>. Whether
-or not it complains, the I<potatoes> text should ignored.
-
-=item C<LE<lt>nameE<gt>> -- a hyperlink
-
-The complicated syntaxes of this code are discussed at length in
-L<perlpod/"Formatting Codes">, and implementation details are
-discussed below, in L</"About LE<lt>...E<gt> Codes">. Parsing the
-contents of LE<lt>content> is tricky. Notably, the content has to be
-checked for whether it looks like a URL, or whether it has to be split
-on literal "|" and/or "/" (in the right order!), and so on,
-I<before> EE<lt>...> codes are resolved.
-
-=item C<EE<lt>escapeE<gt>> -- a character escape
-
-See L<perlpod/"Formatting Codes">, and several points in
-L</Notes on Implementing Pod Processors>.
-
-=item C<SE<lt>textE<gt>> -- text contains non-breaking spaces
-
-This formatting code is syntactically simple, but semantically
-complex. What it means is that each space in the printable
-content of this code signifies a non-breaking space.
-
-Consider:
-
- C<$x ? $y : $z>
-
- S<C<$x ? $y : $z>>
-
-Both signify the monospace (c[ode] style) text consisting of
-"$x", one space, "?", one space, ":", one space, "$z". The
-difference is that in the latter, with the S code, those spaces
-are not "normal" spaces, but instead are non-breaking spaces.
-
-=back
-
-
-If a Pod processor sees any formatting code other than the ones
-listed above (as in "NE<lt>...>", or "QE<lt>...>", etc.), that
-processor must by default treat this as an error.
-A Pod parser may allow a way for particular
-applications to add to the above list of known formatting codes;
-a Pod parser might even allow a way to stipulate, for each additional
-command, whether it requires some form of special processing, as
-LE<lt>...> does.
-
-Future versions of this specification may add additional
-formatting codes.
-
-Historical note: A few older Pod processors would not see a ">" as
-closing a "CE<lt>" code, if the ">" was immediately preceded by
-a "-". This was so that this:
-
- C<$foo->bar>
-
-would parse as equivalent to this:
-
- C<$foo-E<gt>bar>
-
-instead of as equivalent to a "C" formatting code containing
-only "$foo-", and then a "bar>" outside the "C" formatting code. This
-problem has since been solved by the addition of syntaxes like this:
-
- C<< $foo->bar >>
-
-Compliant parsers must not treat "->" as special.
-
-Formatting codes absolutely cannot span paragraphs. If a code is
-opened in one paragraph, and no closing code is found by the end of
-that paragraph, the Pod parser must close that formatting code,
-and should complain (as in "Unterminated I code in the paragraph
-starting at line 123: 'Time objects are not...'"). So these
-two paragraphs:
-
- I<I told you not to do this!
-
- Don't make me say it again!>
-
-...must I<not> be parsed as two paragraphs in italics (with the I
-code starting in one paragraph and starting in another.) Instead,
-the first paragraph should generate a warning, but that aside, the
-above code must parse as if it were:
-
- I<I told you not to do this!>
-
- Don't make me say it again!E<gt>
-
-(In SGMLish jargon, all Pod commands are like block-level
-elements, whereas all Pod formatting codes are like inline-level
-elements.)
-
-
-
-=head1 Notes on Implementing Pod Processors
-
-The following is a long section of miscellaneous requirements
-and suggestions to do with Pod processing.
-
-=over
-
-=item *
-
-Pod formatters should tolerate lines in verbatim blocks that are of
-any length, even if that means having to break them (possibly several
-times, for very long lines) to avoid text running off the side of the
-page. Pod formatters may warn of such line-breaking. Such warnings
-are particularly appropriate for lines are over 100 characters long, which
-are usually not intentional.
-
-=item *
-
-Pod parsers must recognize I<all> of the three well-known newline
-formats: CR, LF, and CRLF. See L<perlport|perlport>.
-
-=item *
-
-Pod parsers should accept input lines that are of any length.
-
-=item *
-
-Since Perl recognizes a Unicode Byte Order Mark at the start of files
-as signaling that the file is Unicode encoded as in UTF-16 (whether
-big-endian or little-endian) or UTF-8, Pod parsers should do the
-same. Otherwise, the character encoding should be understood as
-being UTF-8 if the first highbit byte sequence in the file seems
-valid as a UTF-8 sequence, or otherwise as Latin-1.
-
-Future versions of this specification may specify
-how Pod can accept other encodings. Presumably treatment of other
-encodings in Pod parsing would be as in XML parsing: whatever the
-encoding declared by a particular Pod file, content is to be
-stored in memory as Unicode characters.
-
-=item *
-
-The well known Unicode Byte Order Marks are as follows: if the
-file begins with the two literal byte values 0xFE 0xFF, this is
-the BOM for big-endian UTF-16. If the file begins with the two
-literal byte value 0xFF 0xFE, this is the BOM for little-endian
-UTF-16. If the file begins with the three literal byte values
-0xEF 0xBB 0xBF, this is the BOM for UTF-8.
-
-=for comment
- use bytes; print map sprintf(" 0x%02X", ord $_), split '', "\x{feff}";
- 0xEF 0xBB 0xBF
-
-=for comment
- If toke.c is modified to support UTF-32, add mention of those here.
-
-=item *
-
-A naive but sufficient heuristic for testing the first highbit
-byte-sequence in a BOM-less file (whether in code or in Pod!), to see
-whether that sequence is valid as UTF-8 (RFC 2279) is to check whether
-that the first byte in the sequence is in the range 0xC0 - 0xFD
-I<and> whether the next byte is in the range
-0x80 - 0xBF. If so, the parser may conclude that this file is in
-UTF-8, and all highbit sequences in the file should be assumed to
-be UTF-8. Otherwise the parser should treat the file as being
-in Latin-1. In the unlikely circumstance that the first highbit
-sequence in a truly non-UTF-8 file happens to appear to be UTF-8, one
-can cater to our heuristic (as well as any more intelligent heuristic)
-by prefacing that line with a comment line containing a highbit
-sequence that is clearly I<not> valid as UTF-8. A line consisting
-of simply "#", an e-acute, and any non-highbit byte,
-is sufficient to establish this file's encoding.
-
-=for comment
- If/WHEN some brave soul makes these heuristics into a generic
- text-file class (or PerlIO layer?), we can presumably delete
- mention of these icky details from this file, and can instead
- tell people to just use appropriate class/layer.
- Auto-recognition of newline sequences would be another desirable
- feature of such a class/layer.
- HINT HINT HINT.
-
-=for comment
- "The probability that a string of characters
- in any other encoding appears as valid UTF-8 is low" - RFC2279
-
-=item *
-
-This document's requirements and suggestions about encodings
-do not apply to Pod processors running on non-ASCII platforms,
-notably EBCDIC platforms.
-
-=item *
-
-Pod processors must treat a "=for [label] [content...]" paragraph as
-meaning the same thing as a "=begin [label]" paragraph, content, and
-an "=end [label]" paragraph. (The parser may conflate these two
-constructs, or may leave them distinct, in the expectation that the
-formatter will nevertheless treat them the same.)
-
-=item *
-
-When rendering Pod to a format that allows comments (i.e., to nearly
-any format other than plaintext), a Pod formatter must insert comment
-text identifying its name and version number, and the name and
-version numbers of any modules it might be using to process the Pod.
-Minimal examples:
-
- %% POD::Pod2PS v3.14159, using POD::Parser v1.92
-
- <!-- Pod::HTML v3.14159, using POD::Parser v1.92 -->
-
- {\doccomm generated by Pod::Tree::RTF 3.14159 using Pod::Tree 1.08}
-
- .\" Pod::Man version 3.14159, using POD::Parser version 1.92
-
-Formatters may also insert additional comments, including: the
-release date of the Pod formatter program, the contact address for
-the author(s) of the formatter, the current time, the name of input
-file, the formatting options in effect, version of Perl used, etc.
-
-Formatters may also choose to note errors/warnings as comments,
-besides or instead of emitting them otherwise (as in messages to
-STDERR, or C<die>ing).
-
-=item *
-
-Pod parsers I<may> emit warnings or error messages ("Unknown E code
-EE<lt>zslig>!") to STDERR (whether through printing to STDERR, or
-C<warn>ing/C<carp>ing, or C<die>ing/C<croak>ing), but I<must> allow
-suppressing all such STDERR output, and instead allow an option for
-reporting errors/warnings
-in some other way, whether by triggering a callback, or noting errors
-in some attribute of the document object, or some similarly unobtrusive
-mechanism -- or even by appending a "Pod Errors" section to the end of
-the parsed form of the document.
-
-=item *
-
-In cases of exceptionally aberrant documents, Pod parsers may abort the
-parse. Even then, using C<die>ing/C<croak>ing is to be avoided; where
-possible, the parser library may simply close the input file
-and add text like "*** Formatting Aborted ***" to the end of the
-(partial) in-memory document.
-
-=item *
-
-In paragraphs where formatting codes (like EE<lt>...>, BE<lt>...>)
-are understood (i.e., I<not> verbatim paragraphs, but I<including>
-ordinary paragraphs, and command paragraphs that produce renderable
-text, like "=head1"), literal whitespace should generally be considered
-"insignificant", in that one literal space has the same meaning as any
-(nonzero) number of literal spaces, literal newlines, and literal tabs
-(as long as this produces no blank lines, since those would terminate
-the paragraph). Pod parsers should compact literal whitespace in each
-processed paragraph, but may provide an option for overriding this
-(since some processing tasks do not require it), or may follow
-additional special rules (for example, specially treating
-period-space-space or period-newline sequences).
-
-=item *
-
-Pod parsers should not, by default, try to coerce apostrophe (') and
-quote (") into smart quotes (little 9's, 66's, 99's, etc), nor try to
-turn backtick (`) into anything else but a single backtick character
-(distinct from an open quote character!), nor "--" into anything but
-two minus signs. They I<must never> do any of those things to text
-in CE<lt>...> formatting codes, and never I<ever> to text in verbatim
-paragraphs.
-
-=item *
-
-When rendering Pod to a format that has two kinds of hyphens (-), one
-that's a non-breaking hyphen, and another that's a breakable hyphen
-(as in "object-oriented", which can be split across lines as
-"object-", newline, "oriented"), formatters are encouraged to
-generally translate "-" to non-breaking hyphen, but may apply
-heuristics to convert some of these to breaking hyphens.
-
-=item *
-
-Pod formatters should make reasonable efforts to keep words of Perl
-code from being broken across lines. For example, "Foo::Bar" in some
-formatting systems is seen as eligible for being broken across lines
-as "Foo::" newline "Bar" or even "Foo::-" newline "Bar". This should
-be avoided where possible, either by disabling all line-breaking in
-mid-word, or by wrapping particular words with internal punctuation
-in "don't break this across lines" codes (which in some formats may
-not be a single code, but might be a matter of inserting non-breaking
-zero-width spaces between every pair of characters in a word.)
-
-=item *
-
-Pod parsers should, by default, expand tabs in verbatim paragraphs as
-they are processed, before passing them to the formatter or other
-processor. Parsers may also allow an option for overriding this.
-
-=item *
-
-Pod parsers should, by default, remove newlines from the end of
-ordinary and verbatim paragraphs before passing them to the
-formatter. For example, while the paragraph you're reading now
-could be considered, in Pod source, to end with (and contain)
-the newline(s) that end it, it should be processed as ending with
-(and containing) the period character that ends this sentence.
-
-=item *
-
-Pod parsers, when reporting errors, should make some effort to report
-an approximate line number ("Nested EE<lt>>'s in Paragraph #52, near
-line 633 of Thing/Foo.pm!"), instead of merely noting the paragraph
-number ("Nested EE<lt>>'s in Paragraph #52 of Thing/Foo.pm!"). Where
-this is problematic, the paragraph number should at least be
-accompanied by an excerpt from the paragraph ("Nested EE<lt>>'s in
-Paragraph #52 of Thing/Foo.pm, which begins 'Read/write accessor for
-the CE<lt>interest rate> attribute...'").
-
-=item *
-
-Pod parsers, when processing a series of verbatim paragraphs one
-after another, should consider them to be one large verbatim
-paragraph that happens to contain blank lines. I.e., these two
-lines, which have a blank line between them:
-
- use Foo;
-
- print Foo->VERSION
-
-should be unified into one paragraph ("\tuse Foo;\n\n\tprint
-Foo->VERSION") before being passed to the formatter or other
-processor. Parsers may also allow an option for overriding this.
-
-While this might be too cumbersome to implement in event-based Pod
-parsers, it is straightforward for parsers that return parse trees.
-
-=item *
-
-Pod formatters, where feasible, are advised to avoid splitting short
-verbatim paragraphs (under twelve lines, say) across pages.
-
-=item *
-
-Pod parsers must treat a line with only spaces and/or tabs on it as a
-"blank line" such as separates paragraphs. (Some older parsers
-recognized only two adjacent newlines as a "blank line" but would not
-recognize a newline, a space, and a newline, as a blank line. This
-is noncompliant behavior.)
-
-=item *
-
-Authors of Pod formatters/processors should make every effort to
-avoid writing their own Pod parser. There are already several in
-CPAN, with a wide range of interface styles -- and one of them,
-Pod::Parser, comes with modern versions of Perl.
-
-=item *
-
-Characters in Pod documents may be conveyed either as literals, or by
-number in EE<lt>n> codes, or by an equivalent mnemonic, as in
-EE<lt>eacute> which is exactly equivalent to EE<lt>233>.
-
-Characters in the range 32-126 refer to those well known US-ASCII
-characters (also defined there by Unicode, with the same meaning),
-which all Pod formatters must render faithfully. Characters
-in the ranges 0-31 and 127-159 should not be used (neither as
-literals, nor as EE<lt>number> codes), except for the
-literal byte-sequences for newline (13, 13 10, or 10), and tab (9).
-
-Characters in the range 160-255 refer to Latin-1 characters (also
-defined there by Unicode, with the same meaning). Characters above
-255 should be understood to refer to Unicode characters.
-
-=item *
-
-Be warned
-that some formatters cannot reliably render characters outside 32-126;
-and many are able to handle 32-126 and 160-255, but nothing above
-255.
-
-=item *
-
-Besides the well-known "EE<lt>lt>" and "EE<lt>gt>" codes for
-less-than and greater-than, Pod parsers must understand "EE<lt>sol>"
-for "/" (solidus, slash), and "EE<lt>verbar>" for "|" (vertical bar,
-pipe). Pod parsers should also understand "EE<lt>lchevron>" and
-"EE<lt>rchevron>" as legacy codes for characters 171 and 187, i.e.,
-"left-pointing double angle quotation mark" = "left pointing
-guillemet" and "right-pointing double angle quotation mark" = "right
-pointing guillemet". (These look like little "<<" and ">>", and they
-are now preferably expressed with the HTML/XHTML codes "EE<lt>laquo>"
-and "EE<lt>raquo>".)
-
-=item *
-
-Pod parsers should understand all "EE<lt>html>" codes as defined
-in the entity declarations in the most recent XHTML specification at
-C<www.W3.org>. Pod parsers must understand at least the entities
-that define characters in the range 160-255 (Latin-1). Pod parsers,
-when faced with some unknown "EE<lt>I<identifier>>" code,
-shouldn't simply replace it with nullstring (by default, at least),
-but may pass it through as a string consisting of the literal characters
-E, less-than, I<identifier>, greater-than. Or Pod parsers may offer the
-alternative option of processing such unknown
-"EE<lt>I<identifier>>" codes by firing an event especially
-for such codes, or by adding a special node-type to the in-memory
-document tree. Such "EE<lt>I<identifier>>" may have special meaning
-to some processors, or some processors may choose to add them to
-a special error report.
-
-=item *
-
-Pod parsers must also support the XHTML codes "EE<lt>quot>" for
-character 34 (doublequote, "), "EE<lt>amp>" for character 38
-(ampersand, &), and "EE<lt>apos>" for character 39 (apostrophe, ').
-
-=item *
-
-Note that in all cases of "EE<lt>whatever>", I<whatever> (whether
-an htmlname, or a number in any base) must consist only of
-alphanumeric characters -- that is, I<whatever> must watch
-C<m/\A\w+\z/>. So "EE<lt> 0 1 2 3 >" is invalid, because
-it contains spaces, which aren't alphanumeric characters. This
-presumably does not I<need> special treatment by a Pod processor;
-" 0 1 2 3 " doesn't look like a number in any base, so it would
-presumably be looked up in the table of HTML-like names. Since
-there isn't (and cannot be) an HTML-like entity called " 0 1 2 3 ",
-this will be treated as an error. However, Pod processors may
-treat "EE<lt> 0 1 2 3 >" or "EE<lt>e-acute>" as I<syntactically>
-invalid, potentially earning a different error message than the
-error message (or warning, or event) generated by a merely unknown
-(but theoretically valid) htmlname, as in "EE<lt>qacute>"
-[sic]. However, Pod parsers are not required to make this
-distinction.
-
-=item *
-
-Note that EE<lt>number> I<must not> be interpreted as simply
-"codepoint I<number> in the current/native character set". It always
-means only "the character represented by codepoint I<number> in
-Unicode." (This is identical to the semantics of &#I<number>; in XML.)
-
-This will likely require many formatters to have tables mapping from
-treatable Unicode codepoints (such as the "\xE9" for the e-acute
-character) to the escape sequences or codes necessary for conveying
-such sequences in the target output format. A converter to *roff
-would, for example know that "\xE9" (whether conveyed literally, or via
-a EE<lt>...> sequence) is to be conveyed as "e\\*'".
-Similarly, a program rendering Pod in a Mac OS application window, would
-presumably need to know that "\xE9" maps to codepoint 142 in MacRoman
-encoding that (at time of writing) is native for Mac OS. Such
-Unicode2whatever mappings are presumably already widely available for
-common output formats. (Such mappings may be incomplete! Implementers
-are not expected to bend over backwards in an attempt to render
-Cherokee syllabics, Etruscan runes, Byzantine musical symbols, or any
-of the other weird things that Unicode can encode.) And
-if a Pod document uses a character not found in such a mapping, the
-formatter should consider it an unrenderable character.
-
-=item *
-
-If, surprisingly, the implementor of a Pod formatter can't find a
-satisfactory pre-existing table mapping from Unicode characters to
-escapes in the target format (e.g., a decent table of Unicode
-characters to *roff escapes), it will be necessary to build such a
-table. If you are in this circumstance, you should begin with the
-characters in the range 0x00A0 - 0x00FF, which is mostly the heavily
-used accented characters. Then proceed (as patience permits and
-fastidiousness compels) through the characters that the (X)HTML
-standards groups judged important enough to merit mnemonics
-for. These are declared in the (X)HTML specifications at the
-www.W3.org site. At time of writing (September 2001), the most recent
-entity declaration files are:
-
- http://www.w3.org/TR/xhtml1/DTD/xhtml-lat1.ent
- http://www.w3.org/TR/xhtml1/DTD/xhtml-special.ent
- http://www.w3.org/TR/xhtml1/DTD/xhtml-symbol.ent
-
-Then you can progress through any remaining notable Unicode characters
-in the range 0x2000-0x204D (consult the character tables at
-www.unicode.org), and whatever else strikes your fancy. For example,
-in F<xhtml-symbol.ent>, there is the entry:
-
- <!ENTITY infin "&#8734;"> <!-- infinity, U+221E ISOtech -->
-
-While the mapping "infin" to the character "\x{221E}" will (hopefully)
-have been already handled by the Pod parser, the presence of the
-character in this file means that it's reasonably important enough to
-include in a formatter's table that maps from notable Unicode characters
-to the codes necessary for rendering them. So for a Unicode-to-*roff
-mapping, for example, this would merit the entry:
-
- "\x{221E}" => '\(in',
-
-It is eagerly hoped that in the future, increasing numbers of formats
-(and formatters) will support Unicode characters directly (as (X)HTML
-does with C<&infin;>, C<&#8734;>, or C<&#x221E;>), reducing the need
-for idiosyncratic mappings of Unicode-to-I<my_escapes>.
-
-=item *
-
-It is up to individual Pod formatter to display good judgement when
-confronted with an unrenderable character (which is distinct from an
-unknown EE<lt>thing> sequence that the parser couldn't resolve to
-anything, renderable or not). It is good practice to map Latin letters
-with diacritics (like "EE<lt>eacute>"/"EE<lt>233>") to the corresponding
-unaccented US-ASCII letters (like a simple character 101, "e"), but
-clearly this is often not feasible, and an unrenderable character may
-be represented as "?", or the like. In attempting a sane fallback
-(as from EE<lt>233> to "e"), Pod formatters may use the
-%Latin1Code_to_fallback table in L<Pod::Escapes|Pod::Escapes>, or
-L<Text::Unidecode|Text::Unidecode>, if available.
-
-For example, this Pod text:
-
- magic is enabled if you set C<$Currency> to 'E<euro>'.
-
-may be rendered as:
-"magic is enabled if you set C<$Currency> to 'I<?>'" or as
-"magic is enabled if you set C<$Currency> to 'B<[euro]>'", or as
-"magic is enabled if you set C<$Currency> to '[x20AC]', etc.
-
-A Pod formatter may also note, in a comment or warning, a list of what
-unrenderable characters were encountered.
-
-=item *
-
-EE<lt>...> may freely appear in any formatting code (other than
-in another EE<lt>...> or in an ZE<lt>>). That is, "XE<lt>The
-EE<lt>euro>1,000,000 Solution>" is valid, as is "LE<lt>The
-EE<lt>euro>1,000,000 Solution|Million::Euros>".
-
-=item *
-
-Some Pod formatters output to formats that implement non-breaking
-spaces as an individual character (which I'll call "NBSP"), and
-others output to formats that implement non-breaking spaces just as
-spaces wrapped in a "don't break this across lines" code. Note that
-at the level of Pod, both sorts of codes can occur: Pod can contain a
-NBSP character (whether as a literal, or as a "EE<lt>160>" or
-"EE<lt>nbsp>" code); and Pod can contain "SE<lt>foo
-IE<lt>barE<gt> baz>" codes, where "mere spaces" (character 32) in
-such codes are taken to represent non-breaking spaces. Pod
-parsers should consider supporting the optional parsing of "SE<lt>foo
-IE<lt>barE<gt> baz>" as if it were
-"fooI<NBSP>IE<lt>barE<gt>I<NBSP>baz", and, going the other way, the
-optional parsing of groups of words joined by NBSP's as if each group
-were in a SE<lt>...> code, so that formatters may use the
-representation that maps best to what the output format demands.
-
-=item *
-
-Some processors may find that the C<SE<lt>...E<gt>> code is easiest to
-implement by replacing each space in the parse tree under the content
-of the S, with an NBSP. But note: the replacement should apply I<not> to
-spaces in I<all> text, but I<only> to spaces in I<printable> text. (This
-distinction may or may not be evident in the particular tree/event
-model implemented by the Pod parser.) For example, consider this
-unusual case:
-
- S<L</Autoloaded Functions>>
-
-This means that the space in the middle of the visible link text must
-not be broken across lines. In other words, it's the same as this:
-
- L<"AutoloadedE<160>Functions"/Autoloaded Functions>
-
-However, a misapplied space-to-NBSP replacement could (wrongly)
-produce something equivalent to this:
-
- L<"AutoloadedE<160>Functions"/AutoloadedE<160>Functions>
-
-...which is almost definitely not going to work as a hyperlink (assuming
-this formatter outputs a format supporting hypertext).
-
-Formatters may choose to just not support the S format code,
-especially in cases where the output format simply has no NBSP
-character/code and no code for "don't break this stuff across lines".
-
-=item *
-
-Besides the NBSP character discussed above, implementors are reminded
-of the existence of the other "special" character in Latin-1, the
-"soft hyphen" character, also known as "discretionary hyphen",
-i.e. C<EE<lt>173E<gt>> = C<EE<lt>0xADE<gt>> =
-C<EE<lt>shyE<gt>>). This character expresses an optional hyphenation
-point. That is, it normally renders as nothing, but may render as a
-"-" if a formatter breaks the word at that point. Pod formatters
-should, as appropriate, do one of the following: 1) render this with
-a code with the same meaning (e.g., "\-" in RTF), 2) pass it through
-in the expectation that the formatter understands this character as
-such, or 3) delete it.
-
-For example:
-
- sigE<shy>action
- manuE<shy>script
- JarkE<shy>ko HieE<shy>taE<shy>nieE<shy>mi
-
-These signal to a formatter that if it is to hyphenate "sigaction"
-or "manuscript", then it should be done as
-"sig-I<[linebreak]>action" or "manu-I<[linebreak]>script"
-(and if it doesn't hyphenate it, then the C<EE<lt>shyE<gt>> doesn't
-show up at all). And if it is
-to hyphenate "Jarkko" and/or "Hietaniemi", it can do
-so only at the points where there is a C<EE<lt>shyE<gt>> code.
-
-In practice, it is anticipated that this character will not be used
-often, but formatters should either support it, or delete it.
-
-=item *
-
-If you think that you want to add a new command to Pod (like, say, a
-"=biblio" command), consider whether you could get the same
-effect with a for or begin/end sequence: "=for biblio ..." or "=begin
-biblio" ... "=end biblio". Pod processors that don't understand
-"=for biblio", etc, will simply ignore it, whereas they may complain
-loudly if they see "=biblio".
-
-=item *
-
-Throughout this document, "Pod" has been the preferred spelling for
-the name of the documentation format. One may also use "POD" or
-"pod". For the documentation that is (typically) in the Pod
-format, you may use "pod", or "Pod", or "POD". Understanding these
-distinctions is useful; but obsessing over how to spell them, usually
-is not.
-
-=back
-
-
-
-
-
-=head1 About LE<lt>...E<gt> Codes
-
-As you can tell from a glance at L<perlpod|perlpod>, the LE<lt>...>
-code is the most complex of the Pod formatting codes. The points below
-will hopefully clarify what it means and how processors should deal
-with it.
-
-=over
-
-=item *
-
-In parsing an LE<lt>...> code, Pod parsers must distinguish at least
-four attributes:
-
-=over
-
-=item First:
-
-The link-text. If there is none, this must be undef. (E.g., in
-"LE<lt>Perl Functions|perlfunc>", the link-text is "Perl Functions".
-In "LE<lt>Time::HiRes>" and even "LE<lt>|Time::HiRes>", there is no
-link text. Note that link text may contain formatting.)
-
-=item Second:
-
-The possibly inferred link-text; i.e., if there was no real link
-text, then this is the text that we'll infer in its place. (E.g., for
-"LE<lt>Getopt::Std>", the inferred link text is "Getopt::Std".)
-
-=item Third:
-
-The name or URL, or undef if none. (E.g., in "LE<lt>Perl
-Functions|perlfunc>", the name (also sometimes called the page)
-is "perlfunc". In "LE<lt>/CAVEATS>", the name is undef.)
-
-=item Fourth:
-
-The section (AKA "item" in older perlpods), or undef if none. E.g.,
-in "LE<lt>Getopt::Std/DESCRIPTIONE<gt>", "DESCRIPTION" is the section. (Note
-that this is not the same as a manpage section like the "5" in "man 5
-crontab". "Section Foo" in the Pod sense means the part of the text
-that's introduced by the heading or item whose text is "Foo".)
-
-=back
-
-Pod parsers may also note additional attributes including:
-
-=over
-
-=item Fifth:
-
-A flag for whether item 3 (if present) is a URL (like
-"http://lists.perl.org" is), in which case there should be no section
-attribute; a Pod name (like "perldoc" and "Getopt::Std" are); or
-possibly a man page name (like "crontab(5)" is).
-
-=item Sixth:
-
-The raw original LE<lt>...> content, before text is split on
-"|", "/", etc, and before EE<lt>...> codes are expanded.
-
-=back
-
-(The above were numbered only for concise reference below. It is not
-a requirement that these be passed as an actual list or array.)
-
-For example:
-
- L<Foo::Bar>
- => undef, # link text
- "Foo::Bar", # possibly inferred link text
- "Foo::Bar", # name
- undef, # section
- 'pod', # what sort of link
- "Foo::Bar" # original content
-
- L<Perlport's section on NL's|perlport/Newlines>
- => "Perlport's section on NL's", # link text
- "Perlport's section on NL's", # possibly inferred link text
- "perlport", # name
- "Newlines", # section
- 'pod', # what sort of link
- "Perlport's section on NL's|perlport/Newlines" # orig. content
-
- L<perlport/Newlines>
- => undef, # link text
- '"Newlines" in perlport', # possibly inferred link text
- "perlport", # name
- "Newlines", # section
- 'pod', # what sort of link
- "perlport/Newlines" # original content
-
- L<crontab(5)/"DESCRIPTION">
- => undef, # link text
- '"DESCRIPTION" in crontab(5)', # possibly inferred link text
- "crontab(5)", # name
- "DESCRIPTION", # section
- 'man', # what sort of link
- 'crontab(5)/"DESCRIPTION"' # original content
-
- L</Object Attributes>
- => undef, # link text
- '"Object Attributes"', # possibly inferred link text
- undef, # name
- "Object Attributes", # section
- 'pod', # what sort of link
- "/Object Attributes" # original content
-
- L<http://www.perl.org/>
- => undef, # link text
- "http://www.perl.org/", # possibly inferred link text
- "http://www.perl.org/", # name
- undef, # section
- 'url', # what sort of link
- "http://www.perl.org/" # original content
-
- L<Perl.org|http://www.perl.org/>
- => "Perl.org", # link text
- "http://www.perl.org/", # possibly inferred link text
- "http://www.perl.org/", # name
- undef, # section
- 'url', # what sort of link
- "Perl.org|http://www.perl.org/" # original content
-
-Note that you can distinguish URL-links from anything else by the
-fact that they match C<m/\A\w+:[^:\s]\S*\z/>. So
-C<LE<lt>http://www.perl.comE<gt>> is a URL, but
-C<LE<lt>HTTP::ResponseE<gt>> isn't.
-
-=item *
-
-In case of LE<lt>...> codes with no "text|" part in them,
-older formatters have exhibited great variation in actually displaying
-the link or cross reference. For example, LE<lt>crontab(5)> would render
-as "the C<crontab(5)> manpage", or "in the C<crontab(5)> manpage"
-or just "C<crontab(5)>".
-
-Pod processors must now treat "text|"-less links as follows:
-
- L<name> => L<name|name>
- L</section> => L<"section"|/section>
- L<name/section> => L<"section" in name|name/section>
-
-=item *
-
-Note that section names might contain markup. I.e., if a section
-starts with:
-
- =head2 About the C<-M> Operator
-
-or with:
-
- =item About the C<-M> Operator
-
-then a link to it would look like this:
-
- L<somedoc/About the C<-M> Operator>
-
-Formatters may choose to ignore the markup for purposes of resolving
-the link and use only the renderable characters in the section name,
-as in:
-
- <h1><a name="About_the_-M_Operator">About the <code>-M</code>
- Operator</h1>
-
- ...
-
- <a href="somedoc#About_the_-M_Operator">About the <code>-M</code>
- Operator" in somedoc</a>
-
-=item *
-
-Previous versions of perlpod distinguished C<LE<lt>name/"section"E<gt>>
-links from C<LE<lt>name/itemE<gt>> links (and their targets). These
-have been merged syntactically and semantically in the current
-specification, and I<section> can refer either to a "=headI<n> Heading
-Content" command or to a "=item Item Content" command. This
-specification does not specify what behavior should be in the case
-of a given document having several things all seeming to produce the
-same I<section> identifier (e.g., in HTML, several things all producing
-the same I<anchorname> in <a name="I<anchorname>">...</a>
-elements). Where Pod processors can control this behavior, they should
-use the first such anchor. That is, C<LE<lt>Foo/BarE<gt>> refers to the
-I<first> "Bar" section in Foo.
-
-But for some processors/formats this cannot be easily controlled; as
-with the HTML example, the behavior of multiple ambiguous
-<a name="I<anchorname>">...</a> is most easily just left up to
-browsers to decide.
-
-=item *
-
-In a C<LE<lt>text|...E<gt>> code, text may contain formatting codes
-for formatting or for EE<lt>...> escapes, as in:
-
- L<B<ummE<234>stuff>|...>
-
-For C<LE<lt>...E<gt>> codes without a "name|" part, only
-C<EE<lt>...E<gt>> and C<ZE<lt>E<gt>> codes may occur. That is,
-authors should not use "C<LE<lt>BE<lt>Foo::BarE<gt>E<gt>>".
-
-Note, however, that formatting codes and ZE<lt>>'s can occur in any
-and all parts of an LE<lt>...> (i.e., in I<name>, I<section>, I<text>,
-and I<url>).
-
-Authors must not nest LE<lt>...> codes. For example, "LE<lt>The
-LE<lt>Foo::Bar> man page>" should be treated as an error.
-
-=item *
-
-Note that Pod authors may use formatting codes inside the "text"
-part of "LE<lt>text|name>" (and so on for LE<lt>text|/"sec">).
-
-In other words, this is valid:
-
- Go read L<the docs on C<$.>|perlvar/"$.">
-
-Some output formats that do allow rendering "LE<lt>...>" codes as
-hypertext, might not allow the link-text to be formatted; in
-that case, formatters will have to just ignore that formatting.
-
-=item *
-
-At time of writing, C<LE<lt>nameE<gt>> values are of two types:
-either the name of a Pod page like C<LE<lt>Foo::BarE<gt>> (which
-might be a real Perl module or program in an @INC / PATH
-directory, or a .pod file in those places); or the name of a Unix
-man page, like C<LE<lt>crontab(5)E<gt>>. In theory, C<LE<lt>chmodE<gt>>
-in ambiguous between a Pod page called "chmod", or the Unix man page
-"chmod" (in whatever man-section). However, the presence of a string
-in parens, as in "crontab(5)", is sufficient to signal that what
-is being discussed is not a Pod page, and so is presumably a
-Unix man page. The distinction is of no importance to many
-Pod processors, but some processors that render to hypertext formats
-may need to distinguish them in order to know how to render a
-given C<LE<lt>fooE<gt>> code.
-
-=item *
-
-Previous versions of perlpod allowed for a C<LE<lt>sectionE<gt>> syntax (as in
-C<LE<lt>Object AttributesE<gt>>), which was not easily distinguishable from
-C<LE<lt>nameE<gt>> syntax and for C<LE<lt>"section"E<gt>> which was only
-slightly less ambiguous. This syntax is no longer in the specification, and
-has been replaced by the C<LE<lt>/sectionE<gt>> syntax (where the slash was
-formerly optional). Pod parsers should tolerate the C<LE<lt>"section"E<gt>>
-syntax, for a while at least. The suggested heuristic for distinguishing
-C<LE<lt>sectionE<gt>> from C<LE<lt>nameE<gt>> is that if it contains any
-whitespace, it's a I<section>. Pod processors should warn about this being
-deprecated syntax.
-
-=back
-
-=head1 About =over...=back Regions
-
-"=over"..."=back" regions are used for various kinds of list-like
-structures. (I use the term "region" here simply as a collective
-term for everything from the "=over" to the matching "=back".)
-
-=over
-
-=item *
-
-The non-zero numeric I<indentlevel> in "=over I<indentlevel>" ...
-"=back" is used for giving the formatter a clue as to how many
-"spaces" (ems, or roughly equivalent units) it should tab over,
-although many formatters will have to convert this to an absolute
-measurement that may not exactly match with the size of spaces (or M's)
-in the document's base font. Other formatters may have to completely
-ignore the number. The lack of any explicit I<indentlevel> parameter is
-equivalent to an I<indentlevel> value of 4. Pod processors may
-complain if I<indentlevel> is present but is not a positive number
-matching C<m/\A(\d*\.)?\d+\z/>.
-
-=item *
-
-Authors of Pod formatters are reminded that "=over" ... "=back" may
-map to several different constructs in your output format. For
-example, in converting Pod to (X)HTML, it can map to any of
-<ul>...</ul>, <ol>...</ol>, <dl>...</dl>, or
-<blockquote>...</blockquote>. Similarly, "=item" can map to <li> or
-<dt>.
-
-=item *
-
-Each "=over" ... "=back" region should be one of the following:
-
-=over
-
-=item *
-
-An "=over" ... "=back" region containing only "=item *" commands,
-each followed by some number of ordinary/verbatim paragraphs, other
-nested "=over" ... "=back" regions, "=for..." paragraphs, and
-"=begin"..."=end" regions.
-
-(Pod processors must tolerate a bare "=item" as if it were "=item
-*".) Whether "*" is rendered as a literal asterisk, an "o", or as
-some kind of real bullet character, is left up to the Pod formatter,
-and may depend on the level of nesting.
-
-=item *
-
-An "=over" ... "=back" region containing only
-C<m/\A=item\s+\d+\.?\s*\z/> paragraphs, each one (or each group of them)
-followed by some number of ordinary/verbatim paragraphs, other nested
-"=over" ... "=back" regions, "=for..." paragraphs, and/or
-"=begin"..."=end" codes. Note that the numbers must start at 1
-in each section, and must proceed in order and without skipping
-numbers.
-
-(Pod processors must tolerate lines like "=item 1" as if they were
-"=item 1.", with the period.)
-
-=item *
-
-An "=over" ... "=back" region containing only "=item [text]"
-commands, each one (or each group of them) followed by some number of
-ordinary/verbatim paragraphs, other nested "=over" ... "=back"
-regions, or "=for..." paragraphs, and "=begin"..."=end" regions.
-
-The "=item [text]" paragraph should not match
-C<m/\A=item\s+\d+\.?\s*\z/> or C<m/\A=item\s+\*\s*\z/>, nor should it
-match just C<m/\A=item\s*\z/>.
-
-=item *
-
-An "=over" ... "=back" region containing no "=item" paragraphs at
-all, and containing only some number of
-ordinary/verbatim paragraphs, and possibly also some nested "=over"
-... "=back" regions, "=for..." paragraphs, and "=begin"..."=end"
-regions. Such an itemless "=over" ... "=back" region in Pod is
-equivalent in meaning to a "<blockquote>...</blockquote>" element in
-HTML.
-
-=back
-
-Note that with all the above cases, you can determine which type of
-"=over" ... "=back" you have, by examining the first (non-"=cut",
-non-"=pod") Pod paragraph after the "=over" command.
-
-=item *
-
-Pod formatters I<must> tolerate arbitrarily large amounts of text
-in the "=item I<text...>" paragraph. In practice, most such
-paragraphs are short, as in:
-
- =item For cutting off our trade with all parts of the world
-
-But they may be arbitrarily long:
-
- =item For transporting us beyond seas to be tried for pretended
- offenses
-
- =item He is at this time transporting large armies of foreign
- mercenaries to complete the works of death, desolation and
- tyranny, already begun with circumstances of cruelty and perfidy
- scarcely paralleled in the most barbarous ages, and totally
- unworthy the head of a civilized nation.
-
-=item *
-
-Pod processors should tolerate "=item *" / "=item I<number>" commands
-with no accompanying paragraph. The middle item is an example:
-
- =over
-
- =item 1
-
- Pick up dry cleaning.
-
- =item 2
-
- =item 3
-
- Stop by the store. Get Abba Zabas, Stoli, and cheap lawn chairs.
-
- =back
-
-=item *
-
-No "=over" ... "=back" region can contain headings. Processors may
-treat such a heading as an error.
-
-=item *
-
-Note that an "=over" ... "=back" region should have some
-content. That is, authors should not have an empty region like this:
-
- =over
-
- =back
-
-Pod processors seeing such a contentless "=over" ... "=back" region,
-may ignore it, or may report it as an error.
-
-=item *
-
-Processors must tolerate an "=over" list that goes off the end of the
-document (i.e., which has no matching "=back"), but they may warn
-about such a list.
-
-=item *
-
-Authors of Pod formatters should note that this construct:
-
- =item Neque
-
- =item Porro
-
- =item Quisquam Est
-
- Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
- velit, sed quia non numquam eius modi tempora incidunt ut
- labore et dolore magnam aliquam quaerat voluptatem.
-
- =item Ut Enim
-
-is semantically ambiguous, in a way that makes formatting decisions
-a bit difficult. On the one hand, it could be mention of an item
-"Neque", mention of another item "Porro", and mention of another
-item "Quisquam Est", with just the last one requiring the explanatory
-paragraph "Qui dolorem ipsum quia dolor..."; and then an item
-"Ut Enim". In that case, you'd want to format it like so:
-
- Neque
-
- Porro
-
- Quisquam Est
- Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
- velit, sed quia non numquam eius modi tempora incidunt ut
- labore et dolore magnam aliquam quaerat voluptatem.
-
- Ut Enim
-
-But it could equally well be a discussion of three (related or equivalent)
-items, "Neque", "Porro", and "Quisquam Est", followed by a paragraph
-explaining them all, and then a new item "Ut Enim". In that case, you'd
-probably want to format it like so:
-
- Neque
- Porro
- Quisquam Est
- Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
- velit, sed quia non numquam eius modi tempora incidunt ut
- labore et dolore magnam aliquam quaerat voluptatem.
-
- Ut Enim
-
-But (for the foreseeable future), Pod does not provide any way for Pod
-authors to distinguish which grouping is meant by the above
-"=item"-cluster structure. So formatters should format it like so:
-
- Neque
-
- Porro
-
- Quisquam Est
-
- Qui dolorem ipsum quia dolor sit amet, consectetur, adipisci
- velit, sed quia non numquam eius modi tempora incidunt ut
- labore et dolore magnam aliquam quaerat voluptatem.
-
- Ut Enim
-
-That is, there should be (at least roughly) equal spacing between
-items as between paragraphs (although that spacing may well be less
-than the full height of a line of text). This leaves it to the reader
-to use (con)textual cues to figure out whether the "Qui dolorem
-ipsum..." paragraph applies to the "Quisquam Est" item or to all three
-items "Neque", "Porro", and "Quisquam Est". While not an ideal
-situation, this is preferable to providing formatting cues that may
-be actually contrary to the author's intent.
-
-=back
-
-
-
-=head1 About Data Paragraphs and "=begin/=end" Regions
-
-Data paragraphs are typically used for inlining non-Pod data that is
-to be used (typically passed through) when rendering the document to
-a specific format:
-
- =begin rtf
-
- \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par}
-
- =end rtf
-
-The exact same effect could, incidentally, be achieved with a single
-"=for" paragraph:
-
- =for rtf \par{\pard\qr\sa4500{\i Printed\~\chdate\~\chtime}\par}
-
-(Although that is not formally a data paragraph, it has the same
-meaning as one, and Pod parsers may parse it as one.)
-
-Another example of a data paragraph:
-
- =begin html
-
- I like <em>PIE</em>!
-
- <hr>Especially pecan pie!
-
- =end html
-
-If these were ordinary paragraphs, the Pod parser would try to
-expand the "EE<lt>/em>" (in the first paragraph) as a formatting
-code, just like "EE<lt>lt>" or "EE<lt>eacute>". But since this
-is in a "=begin I<identifier>"..."=end I<identifier>" region I<and>
-the identifier "html" doesn't begin have a ":" prefix, the contents
-of this region are stored as data paragraphs, instead of being
-processed as ordinary paragraphs (or if they began with a spaces
-and/or tabs, as verbatim paragraphs).
-
-As a further example: At time of writing, no "biblio" identifier is
-supported, but suppose some processor were written to recognize it as
-a way of (say) denoting a bibliographic reference (necessarily
-containing formatting codes in ordinary paragraphs). The fact that
-"biblio" paragraphs were meant for ordinary processing would be
-indicated by prefacing each "biblio" identifier with a colon:
-
- =begin :biblio
-
- Wirth, Niklaus. 1976. I<Algorithms + Data Structures =
- Programs.> Prentice-Hall, Englewood Cliffs, NJ.
-
- =end :biblio
-
-This would signal to the parser that paragraphs in this begin...end
-region are subject to normal handling as ordinary/verbatim paragraphs
-(while still tagged as meant only for processors that understand the
-"biblio" identifier). The same effect could be had with:
-
- =for :biblio
- Wirth, Niklaus. 1976. I<Algorithms + Data Structures =
- Programs.> Prentice-Hall, Englewood Cliffs, NJ.
-
-The ":" on these identifiers means simply "process this stuff
-normally, even though the result will be for some special target".
-I suggest that parser APIs report "biblio" as the target identifier,
-but also report that it had a ":" prefix. (And similarly, with the
-above "html", report "html" as the target identifier, and note the
-I<lack> of a ":" prefix.)
-
-Note that a "=begin I<identifier>"..."=end I<identifier>" region where
-I<identifier> begins with a colon, I<can> contain commands. For example:
-
- =begin :biblio
-
- Wirth's classic is available in several editions, including:
-
- =for comment
- hm, check abebooks.com for how much used copies cost.
-
- =over
-
- =item
-
- Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.>
- Teubner, Stuttgart. [Yes, it's in German.]
-
- =item
-
- Wirth, Niklaus. 1976. I<Algorithms + Data Structures =
- Programs.> Prentice-Hall, Englewood Cliffs, NJ.
-
- =back
-
- =end :biblio
-
-Note, however, a "=begin I<identifier>"..."=end I<identifier>"
-region where I<identifier> does I<not> begin with a colon, should not
-directly contain "=head1" ... "=head4" commands, nor "=over", nor "=back",
-nor "=item". For example, this may be considered invalid:
-
- =begin somedata
-
- This is a data paragraph.
-
- =head1 Don't do this!
-
- This is a data paragraph too.
-
- =end somedata
-
-A Pod processor may signal that the above (specifically the "=head1"
-paragraph) is an error. Note, however, that the following should
-I<not> be treated as an error:
-
- =begin somedata
-
- This is a data paragraph.
-
- =cut
-
- # Yup, this isn't Pod anymore.
- sub excl { (rand() > .5) ? "hoo!" : "hah!" }
-
- =pod
-
- This is a data paragraph too.
-
- =end somedata
-
-And this too is valid:
-
- =begin someformat
-
- This is a data paragraph.
-
- And this is a data paragraph.
-
- =begin someotherformat
-
- This is a data paragraph too.
-
- And this is a data paragraph too.
-
- =begin :yetanotherformat
-
- =head2 This is a command paragraph!
-
- This is an ordinary paragraph!
-
- And this is a verbatim paragraph!
-
- =end :yetanotherformat
-
- =end someotherformat
-
- Another data paragraph!
-
- =end someformat
-
-The contents of the above "=begin :yetanotherformat" ...
-"=end :yetanotherformat" region I<aren't> data paragraphs, because
-the immediately containing region's identifier (":yetanotherformat")
-begins with a colon. In practice, most regions that contain
-data paragraphs will contain I<only> data paragraphs; however,
-the above nesting is syntactically valid as Pod, even if it is
-rare. However, the handlers for some formats, like "html",
-will accept only data paragraphs, not nested regions; and they may
-complain if they see (targeted for them) nested regions, or commands,
-other than "=end", "=pod", and "=cut".
-
-Also consider this valid structure:
-
- =begin :biblio
-
- Wirth's classic is available in several editions, including:
-
- =over
-
- =item
-
- Wirth, Niklaus. 1975. I<Algorithmen und Datenstrukturen.>
- Teubner, Stuttgart. [Yes, it's in German.]
-
- =item
-
- Wirth, Niklaus. 1976. I<Algorithms + Data Structures =
- Programs.> Prentice-Hall, Englewood Cliffs, NJ.
-
- =back
-
- Buy buy buy!
-
- =begin html
-
- <img src='wirth_spokesmodeling_book.png'>
-
- <hr>
-
- =end html
-
- Now now now!
-
- =end :biblio
-
-There, the "=begin html"..."=end html" region is nested inside
-the larger "=begin :biblio"..."=end :biblio" region. Note that the
-content of the "=begin html"..."=end html" region is data
-paragraph(s), because the immediately containing region's identifier
-("html") I<doesn't> begin with a colon.
-
-Pod parsers, when processing a series of data paragraphs one
-after another (within a single region), should consider them to
-be one large data paragraph that happens to contain blank lines. So
-the content of the above "=begin html"..."=end html" I<may> be stored
-as two data paragraphs (one consisting of
-"<img src='wirth_spokesmodeling_book.png'>\n"
-and another consisting of "<hr>\n"), but I<should> be stored as
-a single data paragraph (consisting of
-"<img src='wirth_spokesmodeling_book.png'>\n\n<hr>\n").
-
-Pod processors should tolerate empty
-"=begin I<something>"..."=end I<something>" regions,
-empty "=begin :I<something>"..."=end :I<something>" regions, and
-contentless "=for I<something>" and "=for :I<something>"
-paragraphs. I.e., these should be tolerated:
-
- =for html
-
- =begin html
-
- =end html
-
- =begin :biblio
-
- =end :biblio
-
-Incidentally, note that there's no easy way to express a data
-paragraph starting with something that looks like a command. Consider:
-
- =begin stuff
-
- =shazbot
-
- =end stuff
-
-There, "=shazbot" will be parsed as a Pod command "shazbot", not as a data
-paragraph "=shazbot\n". However, you can express a data paragraph consisting
-of "=shazbot\n" using this code:
-
- =for stuff =shazbot
-
-The situation where this is necessary, is presumably quite rare.
-
-Note that =end commands must match the currently open =begin command. That
-is, they must properly nest. For example, this is valid:
-
- =begin outer
-
- X
-
- =begin inner
-
- Y
-
- =end inner
-
- Z
-
- =end outer
-
-while this is invalid:
-
- =begin outer
-
- X
-
- =begin inner
-
- Y
-
- =end outer
-
- Z
-
- =end inner
-
-This latter is improper because when the "=end outer" command is seen, the
-currently open region has the formatname "inner", not "outer". (It just
-happens that "outer" is the format name of a higher-up region.) This is
-an error. Processors must by default report this as an error, and may halt
-processing the document containing that error. A corollary of this is that
-regions cannot "overlap". That is, the latter block above does not represent
-a region called "outer" which contains X and Y, overlapping a region called
-"inner" which contains Y and Z. But because it is invalid (as all
-apparently overlapping regions would be), it doesn't represent that, or
-anything at all.
-
-Similarly, this is invalid:
-
- =begin thing
-
- =end hting
-
-This is an error because the region is opened by "thing", and the "=end"
-tries to close "hting" [sic].
-
-This is also invalid:
-
- =begin thing
-
- =end
-
-This is invalid because every "=end" command must have a formatname
-parameter.
-
-=head1 SEE ALSO
-
-L<perlpod>, L<perlsyn/"PODs: Embedded Documentation">,
-L<podchecker>
-
-=head1 AUTHOR
-
-Sean M. Burke
-
-=cut
-
-