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PERLPODSPEC(1)	       Perl Programmers Reference Guide		PERLPODSPEC(1)

NAME
       perlpodspec - Plain Old Documentation: format specification and notes

DESCRIPTION
       This document is detailed notes on the Pod markup language.  Most
       people will only have to read 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 nice if X did Y"
       versus "it wouldn't really 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 not
       do Y.  I often phrase this as "the parser should, by default, do Y."
       This doesn't 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 may be provided.

Pod Definitions
       Pod is embedded in files, typically Perl source files -- although you
       can write a file that's nothing but Pod.

       A line in a file consists of zero or more non-newline characters,
       terminated by either a newline or the end of the file.

       A 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 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 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).

       (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 no characters at all,
       terminated by a newline.)

       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 "E<32>", which is a formatting code that denotes a
       whitespace character.)

       A 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 Pod formatter (or Pod translator) is a module or
       program that converts Pod to some other format (HTML, plaintext, TeX,
       PostScript, RTF).  A 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 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 "m/\A=cut/" -- or up to the end of the file, if there is no
       "m/\A=cut/" line.

       Within a Pod block, there are 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:

       ·   A command paragraph (also called a "directive").  The first line of
	   this paragraph must match "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

	   Some command paragraphs allow formatting codes in their content
	   (i.e., after the part that matches "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 C<use strict;>?" that
	   it would to an ordinary paragraph -- i.e., formatting codes (like
	   "C<...>") are parsed and presumably formatted appropriately, and
	   whitespace in the form of literal spaces and/or tabs is not
	   significant.

       ·   A verbatim paragraph.  The first line of this paragraph must be a
	   literal space or tab, and this paragraph must not be inside a
	   "=begin identifier", ... "=end identifier" sequence unless
	   "identifier" begins with a colon (":").  That is, if a paragraph
	   starts with a literal space or tab, but is inside a "=begin
	   identifier", ... "=end identifier" region, then it's a data
	   paragraph, unless "identifier" begins with a colon.

	   Whitespace is significant in verbatim paragraphs (although, in
	   processing, tabs are probably expanded).

       ·   An ordinary paragraph.  A paragraph is an ordinary paragraph if its
	   first line matches neither "m/\A=[a-zA-Z]/" nor "m/\A[ \t]/", and
	   if it's not inside a "=begin identifier", ... "=end identifier"
	   sequence unless "identifier" begins with a colon (":").

       ·   A data paragraph.  This is a paragraph that is inside a "=begin
	   identifier" ... "=end identifier" sequence where "identifier" does
	   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 around it.

       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 "m/\A=[a-zA-Z]/".  "[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 identifier" ... "=end identifier" commands stop paragraphs
       that they surround from being parsed as ordinary or verbatim
       paragraphs, if identifier doesn't begin with a colon.  This is
       discussed in detail in the section "About Data Paragraphs and
       "=begin/=end" Regions".

Pod Commands
       This section is intended to supplement and clarify the discussion in
       "Command Paragraph" in perlpod.	These are the currently recognized Pod
       commands:

       "=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!

       "=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.

       "=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 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.

       "=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 "About =over...=back Regions" section,
	   further below.  Formatting codes are not expanded.  Examples:

	     =over 3

	     =over 3.5

	     =over

       "=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 "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.

       "=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.

       "=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" does begin
	   with a colon, then non-command paragraphs are ordinary paragraphs
	   or data paragraphs.	This is discussed in detail in the section
	   "About Data Paragraphs and "=begin/=end" Regions".

	   It is advised that formatnames match the regexp
	   "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".

       "=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 "About Data Paragraphs and "=begin/=end" Regions".

       "=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" 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.

       "=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 encodingname, which must be an encoding
	   name that Encode recognizes.	 (Encode's list of supported
	   encodings, in 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).

       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.

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:

       ·   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>

       ·   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 "C<<<" and
	   before the ">>" (or whatever letter) are 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.

       In parsing Pod, a notably tricky part is the correct parsing of
       (potentially nested!) formatting codes.	Implementors should consult
       the code in the "parse_text" routine in Pod::Parser as an example of a
       correct implementation.

       "I<text>" -- italic text
	   See the brief discussion in "Formatting Codes" in perlpod.

       "B<text>" -- bold text
	   See the brief discussion in "Formatting Codes" in perlpod.

       "C<code>" -- code text
	   See the brief discussion in "Formatting Codes" in perlpod.

       "F<filename>" -- style for filenames
	   See the brief discussion in "Formatting Codes" in perlpod.

       "X<topic name>" -- an index entry
	   See the brief discussion in "Formatting Codes" in perlpod.

	   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.

       "Z<>" -- a null (zero-effect) formatting code
	   Discussed briefly in "Formatting Codes" in perlpod.

	   This code is unusual is that it should have no content.  That is, a
	   processor may complain if it sees "Z<potatoes>".  Whether or not it
	   complains, the potatoes text should ignored.

       "L<name>" -- a hyperlink
	   The complicated syntaxes of this code are discussed at length in
	   "Formatting Codes" in perlpod, and implementation details are
	   discussed below, in "About L<...> Codes".  Parsing the contents of
	   L<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, before
	   E<...> codes are resolved.

       "E<escape>" -- a character escape
	   See "Formatting Codes" in perlpod, and several points in "Notes on
	   Implementing Pod Processors".

       "S<text>" -- 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.

       If a Pod processor sees any formatting code other than the ones listed
       above (as in "N<...>", or "Q<...>", 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 L<...> 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 "C<" 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 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.)

Notes on Implementing Pod Processors
       The following is a long section of miscellaneous requirements and
       suggestions to do with Pod processing.

       ·   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.

       ·   Pod parsers must recognize all of the three well-known newline
	   formats: CR, LF, and CRLF.  See perlport.

       ·   Pod parsers should accept input lines that are of any length.

       ·   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.

       ·   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.

       ·   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 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
	   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.

       ·   This document's requirements and suggestions about encodings do not
	   apply to Pod processors running on non-ASCII platforms, notably
	   EBCDIC platforms.

       ·   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.)

       ·   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 "die"ing).

       ·   Pod parsers may emit warnings or error messages ("Unknown E code
	   E<zslig>!") to STDERR (whether through printing to STDERR, or
	   "warn"ing/"carp"ing, or "die"ing/"croak"ing), but 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.

       ·   In cases of exceptionally aberrant documents, Pod parsers may abort
	   the parse.  Even then, using "die"ing/"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.

       ·   In paragraphs where formatting codes (like E<...>, B<...>) are
	   understood (i.e., not verbatim paragraphs, but 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).

       ·   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 must never do any of those
	   things to text in C<...> formatting codes, and never ever to text
	   in verbatim paragraphs.

       ·   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.

       ·   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.)

       ·   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.

       ·   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.

       ·   Pod parsers, when reporting errors, should make some effort to
	   report an approximate line number ("Nested E<>'s in Paragraph #52,
	   near line 633 of Thing/Foo.pm!"), instead of merely noting the
	   paragraph number ("Nested E<>'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 E<>'s in Paragraph #52 of Thing/Foo.pm, which begins
	   'Read/write accessor for the C<interest rate> attribute...'").

       ·   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.

       ·   Pod formatters, where feasible, are advised to avoid splitting
	   short verbatim paragraphs (under twelve lines, say) across pages.

       ·   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.)

       ·   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.

       ·   Characters in Pod documents may be conveyed either as literals, or
	   by number in E<n> codes, or by an equivalent mnemonic, as in
	   E<eacute> which is exactly equivalent to E<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 E<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.

       ·   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.

       ·   Besides the well-known "E<lt>" and "E<gt>" codes for less-than and
	   greater-than, Pod parsers must understand "E<sol>" for "/"
	   (solidus, slash), and "E<verbar>" for "|" (vertical bar, pipe).
	   Pod parsers should also understand "E<lchevron>" and "E<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 "E<laquo>" and
	   "E<raquo>".)

       ·   Pod parsers should understand all "E<html>" codes as defined in the
	   entity declarations in the most recent XHTML specification at
	   "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 "E<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, identifier, greater-than.  Or Pod parsers
	   may offer the alternative option of processing such unknown
	   "E<identifier>" codes by firing an event especially for such codes,
	   or by adding a special node-type to the in-memory document tree.
	   Such "E<identifier>" may have special meaning to some processors,
	   or some processors may choose to add them to a special error
	   report.

       ·   Pod parsers must also support the XHTML codes "E<quot>" for
	   character 34 (doublequote, "), "E<amp>" for character 38
	   (ampersand, &), and "E<apos>" for character 39 (apostrophe, ').

       ·   Note that in all cases of "E<whatever>", whatever (whether an
	   htmlname, or a number in any base) must consist only of
	   alphanumeric characters -- that is, whatever must watch
	   "m/\A\w+\z/".  So "E< 0 1 2 3 >" is invalid, because it contains
	   spaces, which aren't alphanumeric characters.  This presumably does
	   not 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 "E< 0 1 2 3 >" or
	   "E<e-acute>" as 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 "E<qacute>" [sic].  However, Pod parsers are not
	   required to make this distinction.

       ·   Note that E<number> must not be interpreted as simply "codepoint
	   number in the current/native character set".	 It always means only
	   "the character represented by codepoint number in Unicode."	(This
	   is identical to the semantics of &#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 E<...> 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.

       ·   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 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 "∞", "∞", or "∞"),
	   reducing the need for idiosyncratic mappings of
	   Unicode-to-my_escapes.

       ·   It is up to individual Pod formatter to display good judgement when
	   confronted with an unrenderable character (which is distinct from
	   an unknown E<thing> sequence that the parser couldn't resolve to
	   anything, renderable or not).  It is good practice to map Latin
	   letters with diacritics (like "E<eacute>"/"E<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 E<233> to "e"), Pod formatters
	   may use the %Latin1Code_to_fallback table in Pod::Escapes, or
	   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 $Currency to '?'"
	   or as "magic is enabled if you set $Currency to '[euro]'", or as
	   "magic is enabled if you set $Currency to '[x20AC]', etc.

	   A Pod formatter may also note, in a comment or warning, a list of
	   what unrenderable characters were encountered.

       ·   E<...> may freely appear in any formatting code (other than in
	   another E<...> or in an Z<>).  That is, "X<The E<euro>1,000,000
	   Solution>" is valid, as is "L<The E<euro>1,000,000
	   Solution|Million::Euros>".

       ·   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 "E<160>" or
	   "E<nbsp>" code); and Pod can contain "S<foo I<bar> 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 "S<foo I<bar> baz>" as if it
	   were "fooNBSPI<bar>NBSPbaz", and, going the other way, the optional
	   parsing of groups of words joined by NBSP's as if each group were
	   in a S<...> code, so that formatters may use the representation
	   that maps best to what the output format demands.

       ·   Some processors may find that the "S<...>" 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 not to spaces in all text, but only to spaces in 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".

       ·   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. "E<173>" = "E<0xAD>" = "E<shy>").  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-[linebreak]action"
	   or "manu-[linebreak]script" (and if it doesn't hyphenate it, then
	   the "E<shy>" 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 "E<shy>" code.

	   In practice, it is anticipated that this character will not be used
	   often, but formatters should either support it, or delete it.

       ·   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".

       ·   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.

About L<;...> Codes
       As you can tell from a glance at perlpod, the L<...> 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.

       ·   In parsing an L<...> code, Pod parsers must distinguish at least
	   four attributes:

	   First:
	       The link-text.  If there is none, this must be undef.  (E.g.,
	       in "L<Perl Functions|perlfunc>", the link-text is "Perl
	       Functions".  In "L<Time::HiRes>" and even "L<|Time::HiRes>",
	       there is no link text.  Note that link text may contain
	       formatting.)

	   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 "L<Getopt::Std>", the inferred link text is
	       "Getopt::Std".)

	   Third:
	       The name or URL, or undef if none.  (E.g., in "L<Perl
	       Functions|perlfunc>", the name -- also sometimes called the
	       page -- is "perlfunc".  In "L</CAVEATS>", the name is undef.)

	   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".)

	   Pod parsers may also note additional attributes including:

	   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).

	   Sixth:
	       The raw original L<...> content, before text is split on "|",
	       "/", etc, and before E<...> codes are expanded.

	   (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 "m/\A\w+:[^:\s]\S*\z/".	 So
	   "L<http://www.perl.com>" is a URL, but "L<HTTP::Response>" isn't.

       ·   In case of L<...> codes with no "text|" part in them, older
	   formatters have exhibited great variation in actually displaying
	   the link or cross reference.	 For example, L<crontab(5)> would
	   render as "the crontab(5) manpage", or "in the crontab(5) manpage"
	   or just "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>

       ·   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>

       ·   Previous versions of perlpod distinguished "L<name/"section">"
	   links from "L<name/item>" links (and their targets).	 These have
	   been merged syntactically and semantically in the current
	   specification, and section can refer either to a "=headn 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 section identifier (e.g., in HTML, several things all
	   producing the same anchorname in <a name="anchorname">...</a>
	   elements).  Where Pod processors can control this behavior, they
	   should use the first such anchor.  That is, "L<Foo/Bar>" refers to
	   the 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="anchorname">...</a> is most easily just left up to browsers
	   to decide.

       ·   Authors wanting to link to a particular (absolute) URL, must do so
	   only with "L<scheme:...>" codes (like L<http://www.perl.org>), and
	   must not attempt "L<Some Site Name|scheme:...>" codes.  This
	   restriction avoids many problems in parsing and rendering L<...>
	   codes.

       ·   In a "L<text|...>" code, text may contain formatting codes for
	   formatting or for E<...> escapes, as in:

	     L<B<ummE<234>stuff>|...>

	   For "L<...>" codes without a "name|" part, only "E<...>" and "Z<>"
	   codes may occur -- no other formatting codes.  That is, authors
	   should not use ""L<B<Foo::Bar>>"".

	   Note, however, that formatting codes and Z<>'s can occur in any and
	   all parts of an L<...> (i.e., in name, section, text, and url).

	   Authors must not nest L<...> codes.	For example, "L<The
	   L<Foo::Bar> man page>" should be treated as an error.

       ·   Note that Pod authors may use formatting codes inside the "text"
	   part of "L<text|name>" (and so on for L<text|/"sec">).

	   In other words, this is valid:

	     Go read L<the docs on C<$.>|perlvar/"$.">

	   Some output formats that do allow rendering "L<...>" codes as
	   hypertext, might not allow the link-text to be formatted; in that
	   case, formatters will have to just ignore that formatting.

       ·   At time of writing, "L<name>" values are of two types: either the
	   name of a Pod page like "L<Foo::Bar>" (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
	   "L<crontab(5)>".  In theory, "L<chmod>" 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 "L<foo>" code.

       ·   Previous versions of perlpod allowed for a "L<section>" syntax (as
	   in "L<Object Attributes>"), which was not easily distinguishable
	   from "L<name>" syntax.  This syntax is no longer in the
	   specification, and has been replaced by the "L<"section">" syntax
	   (where the quotes were formerly optional).  Pod parsers should
	   tolerate the "L<section>" syntax, for a while at least.  The
	   suggested heuristic for distinguishing "L<section>" from "L<name>"
	   is that if it contains any whitespace, it's a section.  Pod
	   processors may warn about this being deprecated syntax.

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".)

       ·   The non-zero numeric indentlevel in "=over 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 indentlevel
	   parameter is equivalent to an indentlevel value of 4.  Pod
	   processors may complain if indentlevel is present but is not a
	   positive number matching "m/\A(\d*\.)?\d+\z/".

       ·   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>.

       ·   Each "=over" ... "=back" region should be one of the following:

	   ·   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.

	   ·   An "=over" ... "=back" region containing only
	       "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.)

	   ·   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
	       "m/\A=item\s+\d+\.?\s*\z/" or "m/\A=item\s+\*\s*\z/", nor
	       should it match just "m/\A=item\s*\z/".

	   ·   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.

	   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.

       ·   Pod formatters must tolerate arbitrarily large amounts of text in
	   the "=item 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.

       ·   Pod processors should tolerate "=item *" / "=item 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

       ·   No "=over" ... "=back" region can contain headings.	Processors may
	   treat such a heading as an error.

       ·   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.

       ·   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.

       ·   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.

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 "E</em>" (in the first paragraph) as a formatting code, just like
       "E<lt>" or "E<eacute>".	But since this is in a "=begin
       identifier"..."=end identifier" region 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 lack of a
       ":" prefix.)

       Note that a "=begin identifier"..."=end identifier" region where
       identifier begins with a colon, 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 identifier"..."=end identifier" region where
       identifier does 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 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 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 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") 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" may be stored as two data
       paragraphs (one consisting of "<img
       src='wirth_spokesmodeling_book.png'>\n" and another consisting of
       "<hr>\n"), but 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 something"..."=end
       something" regions, empty "=begin :something"..."=end :something"
       regions, and contentless "=for something" and "=for :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.

SEE ALSO
       perlpod, "PODs: Embedded Documentation" in perlsyn, podchecker

AUTHOR
       Sean M. Burke

perl v5.10.1			  2009-05-26			PERLPODSPEC(1)
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