--- /dev/null
+
+=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 wordcounting it, 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 data 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 black 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"
+
+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/>. 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.
+
+=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.
+
+=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 nonbreaking 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, "$z". The
+difference is that in the latter, with the S code, those spaces
+are not "normal" spaces, but instead are nonbreaking spaces.
+
+=back
+
+
+If a Pod processor sees any formatting code other than the ones
+listed above (as in "NE<lt>...>", or "QE<lt>...>", etc.), that
+processor must by default treat this as an error.
+A Pod parser may allow a way for particular
+applications to add to the above list of known formatting codes;
+a Pod parser might even allow a way to stipulate, for each additional
+command, whether it requires some form of special processing, as
+LE<lt>...> does.
+
+Future versions of this specification may add additional
+formatting codes.
+
+Historical note: A few older Pod processors would not see a ">" as
+closing a "CE<lt>" code, if the ">" was immediately preceded by
+a "-". This was so that this:
+
+ C<$foo->bar>
+
+would parse as equivalent to this:
+
+ C<$foo-E<lt>bar>
+
+instead of as equivalent to a "C" formatting code containing
+only "$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 UTF32, 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 openquote 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 nonbreaking 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 nonbreaking 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 "∞"> <!-- 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<∞>, C<∞>, or C<∞>), reducing the need
+for idiosyncratic mappings of Unicode-to-I<my_escapes>.
+
+=item *
+
+It is up to individual Pod formatter to display good judgment 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 nonbreaking
+spaces as an individual character (which I'll call "NBSP"), and
+others output to formats that implement nonbreaking 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 nonbreaking 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 L<Getopt::Std/DESCRIPTION>, "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
+
+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 *
+
+Authors wanting to link to a particular (absolute) URL, must do so
+only with "LE<lt>scheme:...>" codes (like
+LE<lt>http://www.perl.org>), and must not attempt "LE<lt>Some Site
+Name|scheme:...>" codes. This restriction avoids many problems
+in parsing and rendering LE<lt>...> codes.
+
+=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 -- no
+other formatting codes. 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. This syntax is no longer in the
+specification, and has been replaced by the C<LE<lt>"section"E<gt>> syntax
+(where the quotes were formerly optional). Pod parsers should tolerate
+the C<LE<lt>sectionE<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
+may 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 forseeable 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" -- i.e., 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
+
+
projects / dh-make-perl / blobdiff