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NAME    [Toc]    [Back]

       perlpodspec - Plain Old Documentation: format specification
 and notes

DESCRIPTION    [Toc]    [Back]

       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    [Toc]    [Back]

       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 systemspecific
 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 wordcounting it, scanning for index
       points, etc.).

       Pod content is contained in Pod blocks.  A Pod block
       starts with a line that matches <m/0        tinues  up  to
the  next line that matches "m/0       up to the end of the file,
if there is no "m/1       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:

       o   A command paragraph (also called a "directive").  The
           first line of this paragraph must match
           "m/0           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
             =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.

       o   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

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

       o   An ordinary paragraph.  A paragraph is an ordinary
           paragraph if its first line matches neither
           "m/0begin identifier", ... "=end identifier"
           sequence unless "identifier" begins with a colon

       o   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




       Here, "=head1 Foo" and "=cut" are command paragraphs
       because the first line of each matches "m/1
       "[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
       data 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    [Toc]    [Back]

       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!

           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:


             This is a plain Pod paragraph.

             =pod This text is ignored.

           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.


             =cut The documentation ends here.

             # 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.

           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


           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 14

             =item   3.

             =item C<< $thing->stuff(I<dodad>) >>

             =item  For  transporting  us beyond seas to be tried
for pretended

             =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
             unworthy the head of a civilized nation.

           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/0           ipate 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


                =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 encod-
           ingname, which must be an encoding name that Encoding
           recognizes.  (Encoding's list of supported encodings,
           in Encoding::Supported, is useful here.)  If the Pod
           parser cannot decode the declared encoding, it should
           emit a warning and may abort parsing the document

           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 "=use utf8" line, and later on another "=use
           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

       Future versions of this specification may add additional

Pod Formatting Codes    [Toc]    [Back]

       (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

       There are two syntaxes for formatting codes:

       o   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>

       o   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 >>>

           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

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

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

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

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

           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.


               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:


       would parse as equivalent to this:

       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    [Toc]    [Back]

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

       o   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

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

       o   Pod parsers should accept input lines that are of any

       o   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.

       o   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.

       o   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.

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

       o   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.)

       o   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 -->

             {occomm generated by  Pod::Tree::RTF  3.14159  using
Pod::Tree 1.08}


           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).

       o   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

       o   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.

       o   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).

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

       o   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.

       o   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.)

       o   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.

       o   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
       o   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...'").

       o   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 ("use
           Foo;0rint 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.

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

       o   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.)

       o   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.

       o   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

           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.

       o   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.

       o   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>".)

       o   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 nodetype
 to the in-memory document tree.  Such "E<identi-
           fier>" may have special meaning to some processors, or
           some processors may choose to add them to a special
           error report.

       o   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, ').

       o   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/1           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.

       o   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 " 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 " (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 " 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.

       o   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:


           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-sym-
           bol.ent, there is the entry:

             <!ENTITY  infin     "&#8734;"> <!-- infinity, U+221E
ISOtech -->

           While the mapping "infin" to the character "}"

           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:

             "}" => '',

           It is eagerly hoped that in the future, increasing
           numbers of formats (and formatters) will support Unicode
 characters directly (as (X)HTML does with
           "&infin;", "&#8734;", or "&#x221E;"), reducing the
           need for idiosyncratic mappings of Unicode-to-my_escapes.

       o   It is up to individual Pod formatter to display good
           judgment 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

       o   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>".

       o   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.

       o   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:

           ...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".

       o   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:

             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.

       o   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".

       o   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.

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

               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

               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

               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.)

               The section (AKA "item" in older perlpods), or
               undef if none.  E.g., in "DESCRIPTION" in
               Getopt::Std, "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

           Pod parsers may also note additional attributes

               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).
               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:

               =>  undef,                          # link text
                   "Foo::Bar",                     # possibly inferred link text
                   "Foo::Bar",                     # name
                   undef,                          # section
                   'pod',                          # what sort of
                   "Foo::Bar"                        #   original

             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
                   "Perlport's section on NL's|perlport/Newlines"
# orig. content

               =>  undef,                          # link text
                   '"Newlines" in perlport',       # possibly inferred link text
                   "perlport",                     # name
                   "Newlines",                     # section
                   'pod',                          # what sort of
                   "perlport/Newlines"               #   original

               =>  undef,                          # link text
                   '"DESCRIPTION" in crontab(5)',  # possibly inferred link text
                   "crontab(5)",                   # name
                   "DESCRIPTION",                  # section
                   'man',                          # what sort of
                   'crontab(5)/"DESCRIPTION"'        #   original

             L</Object Attributes>
               =>  undef,                          # link text
                   '"Object Attributes"',          # possibly inferred link text
                   undef,                          # name
                   "Object Attributes",            # section
                   'pod',                          # what sort of
                   "/Object   Attributes"             #  original
               =>  undef,                          # link text
                   "http://www.perl.org/",         # possibly inferred link text
                   "http://www.perl.org/",         # name
                   undef,                          # section
                   'url',                          # what sort of
                   "http://www.perl.org/"            #   original

           Note that you can distinguish URL-links from anything
           else by the fact that they match
           "m/1             is  a  URL,  but  "L<HTTP::Response>"

       o   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

           Pod processors must now treat "text|"-less links as

             L<name>         =>  L<name|name>
             L</section>     =>  L<"section"|/section>
             L<name/section>  =>   L<"section"  in name|name/section>

       o   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


             <a   href="somedoc#About_the_-M_Operator">About  the
             Operator" in somedoc</a>

       o   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="anchor-
           name">...</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.

       o   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.

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


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

           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

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

           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.

       o   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.

       o   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 

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