friendica/library/markdown.php

<?php
#
# Markdown Extra  -  A text-to-HTML conversion tool for web writers
#
# PHP Markdown & Extra
# Copyright (c) 2004-2012 Michel Fortin  
# <http://michelf.com/projects/php-markdown/>
#
# Original Markdown
# Copyright (c) 2004-2006 John Gruber  
# <http://daringfireball.net/projects/markdown/>
#


define( 'MARKDOWN_VERSION',  "1.0.1o" ); # Sun 8 Jan 2012
define( 'MARKDOWNEXTRA_VERSION',  "1.2.5" ); # Sun 8 Jan 2012


#
# Global default settings:
#

# Change to ">" for HTML output
@define( 'MARKDOWN_EMPTY_ELEMENT_SUFFIX',  " />");

# Define the width of a tab for code blocks.
@define( 'MARKDOWN_TAB_WIDTH',     4 );

# Optional title attribute for footnote links and backlinks.
@define( 'MARKDOWN_FN_LINK_TITLE',         "" );
@define( 'MARKDOWN_FN_BACKLINK_TITLE',     "" );

# Optional class attribute for footnote links and backlinks.
@define( 'MARKDOWN_FN_LINK_CLASS',         "" );
@define( 'MARKDOWN_FN_BACKLINK_CLASS',     "" );


#
# WordPress settings:
#

# Change to false to remove Markdown from posts and/or comments.
@define( 'MARKDOWN_WP_POSTS',      true );
@define( 'MARKDOWN_WP_COMMENTS',   true );



### Standard Function Interface ###

@define( 'MARKDOWN_PARSER_CLASS',  'MarkdownExtra_Parser' );

function Markdown($text) {
#
# Initialize the parser and return the result of its transform method.
#
	# Setup static parser variable.
	static $parser;
	if (!isset($parser)) {
		$parser_class = MARKDOWN_PARSER_CLASS;
		$parser = new $parser_class;
	}

	# Transform text using parser.
	return $parser->transform($text);
}


### WordPress Plugin Interface ###

/*
Plugin Name: Markdown Extra
Plugin URI: http://michelf.com/projects/php-markdown/
Description: <a href="http://daringfireball.net/projects/markdown/syntax">Markdown syntax</a> allows you to write using an easy-to-read, easy-to-write plain text format. Based on the original Perl version by <a href="http://daringfireball.net/">John Gruber</a>. <a href="http://michelf.com/projects/php-markdown/">More...</a>
Version: 1.2.5
Author: Michel Fortin
Author URI: http://michelf.com/
*/

if (isset($wp_version)) {
	# More details about how it works here:
	# <http://michelf.com/weblog/2005/wordpress-text-flow-vs-markdown/>
	
	# Post content and excerpts
	# - Remove WordPress paragraph generator.
	# - Run Markdown on excerpt, then remove all tags.
	# - Add paragraph tag around the excerpt, but remove it for the excerpt rss.
	if (MARKDOWN_WP_POSTS) {
		remove_filter('the_content',     'wpautop');
        remove_filter('the_content_rss', 'wpautop');
		remove_filter('the_excerpt',     'wpautop');
		add_filter('the_content',     'mdwp_MarkdownPost', 6);
        add_filter('the_content_rss', 'mdwp_MarkdownPost', 6);
		add_filter('get_the_excerpt', 'mdwp_MarkdownPost', 6);
		add_filter('get_the_excerpt', 'trim', 7);
		add_filter('the_excerpt',     'mdwp_add_p');
		add_filter('the_excerpt_rss', 'mdwp_strip_p');
		
		remove_filter('content_save_pre',  'balanceTags', 50);
		remove_filter('excerpt_save_pre',  'balanceTags', 50);
		add_filter('the_content',  	  'balanceTags', 50);
		add_filter('get_the_excerpt', 'balanceTags', 9);
	}
	
	# Add a footnote id prefix to posts when inside a loop.
	function mdwp_MarkdownPost($text) {
		static $parser;
		if (!$parser) {
			$parser_class = MARKDOWN_PARSER_CLASS;
			$parser = new $parser_class;
		}
		if (is_single() || is_page() || is_feed()) {
			$parser->fn_id_prefix = "";
		} else {
			$parser->fn_id_prefix = get_the_ID() . ".";
		}
		return $parser->transform($text);
	}
	
	# Comments
	# - Remove WordPress paragraph generator.
	# - Remove WordPress auto-link generator.
	# - Scramble important tags before passing them to the kses filter.
	# - Run Markdown on excerpt then remove paragraph tags.
	if (MARKDOWN_WP_COMMENTS) {
		remove_filter('comment_text', 'wpautop', 30);
		remove_filter('comment_text', 'make_clickable');
		add_filter('pre_comment_content', 'Markdown', 6);
		add_filter('pre_comment_content', 'mdwp_hide_tags', 8);
		add_filter('pre_comment_content', 'mdwp_show_tags', 12);
		add_filter('get_comment_text',    'Markdown', 6);
		add_filter('get_comment_excerpt', 'Markdown', 6);
		add_filter('get_comment_excerpt', 'mdwp_strip_p', 7);
	
		global $mdwp_hidden_tags, $mdwp_placeholders;
		$mdwp_hidden_tags = explode(' ',
			'<p> </p> <pre> </pre> <ol> </ol> <ul> </ul> <li> </li>');
		$mdwp_placeholders = explode(' ', str_rot13(
			'pEj07ZbbBZ U1kqgh4w4p pre2zmeN6K QTi31t9pre ol0MP1jzJR '.
			'ML5IjmbRol ulANi1NsGY J7zRLJqPul liA8ctl16T K9nhooUHli'));
	}
	
	function mdwp_add_p($text) {
		if (!preg_match('{^$|^<(p|ul|ol|dl|pre|blockquote)>}i', $text)) {
			$text = '<p>'.$text.'</p>';
			$text = preg_replace('{\n{2,}}', "</p>\n\n<p>", $text);
		}
		return $text;
	}
	
	function mdwp_strip_p($t) { return preg_replace('{</?p>}i', '', $t); }

	function mdwp_hide_tags($text) {
		global $mdwp_hidden_tags, $mdwp_placeholders;
		return str_replace($mdwp_hidden_tags, $mdwp_placeholders, $text);
	}
	function mdwp_show_tags($text) {
		global $mdwp_hidden_tags, $mdwp_placeholders;
		return str_replace($mdwp_placeholders, $mdwp_hidden_tags, $text);
	}
}


### bBlog Plugin Info ###

function identify_modifier_markdown() {
	return array(
		'name' => 'markdown',
		'type' => 'modifier',
		'nicename' => 'PHP Markdown Extra',
		'description' => 'A text-to-HTML conversion tool for web writers',
		'authors' => 'Michel Fortin and John Gruber',
		'licence' => 'GPL',
		'version' => MARKDOWNEXTRA_VERSION,
		'help' => '<a href="http://daringfireball.net/projects/markdown/syntax">Markdown syntax</a> allows you to write using an easy-to-read, easy-to-write plain text format. Based on the original Perl version by <a href="http://daringfireball.net/">John Gruber</a>. <a href="http://michelf.com/projects/php-markdown/">More...</a>',
		);
}


### Smarty Modifier Interface ###

function smarty_modifier_markdown($text) {
	return Markdown($text);
}


### Textile Compatibility Mode ###

# Rename this file to "classTextile.php" and it can replace Textile everywhere.

if (strcasecmp(substr(__FILE__, -16), "classTextile.php") == 0) {
	# Try to include PHP SmartyPants. Should be in the same directory.
	@include_once 'smartypants.php';
	# Fake Textile class. It calls Markdown instead.
	class Textile {
		function TextileThis($text, $lite='', $encode='') {
			if ($lite == '' && $encode == '')    $text = Markdown($text);
			if (function_exists('SmartyPants'))  $text = SmartyPants($text);
			return $text;
		}
		# Fake restricted version: restrictions are not supported for now.
		function TextileRestricted($text, $lite='', $noimage='') {
			return $this->TextileThis($text, $lite);
		}
		# Workaround to ensure compatibility with TextPattern 4.0.3.
		function blockLite($text) { return $text; }
	}
}



#
# Markdown Parser Class
#

class Markdown_Parser {

	# Regex to match balanced [brackets].
	# Needed to insert a maximum bracked depth while converting to PHP.
	var $nested_brackets_depth = 6;
	var $nested_brackets_re;
	
	var $nested_url_parenthesis_depth = 4;
	var $nested_url_parenthesis_re;

	# Table of hash values for escaped characters:
	var $escape_chars = '\`*_{}[]()>#+-.!';
	var $escape_chars_re;

	# Change to ">" for HTML output.
	var $empty_element_suffix = MARKDOWN_EMPTY_ELEMENT_SUFFIX;
	var $tab_width = MARKDOWN_TAB_WIDTH;
	
	# Change to `true` to disallow markup or entities.
	var $no_markup = false;
	var $no_entities = false;
	
	# Predefined urls and titles for reference links and images.
	var $predef_urls = array();
	var $predef_titles = array();


	function Markdown_Parser() {
	#
	# Constructor function. Initialize appropriate member variables.
	#
		$this->_initDetab();
		$this->prepareItalicsAndBold();
	
		$this->nested_brackets_re = 
			str_repeat('(?>[^\[\]]+|\[', $this->nested_brackets_depth).
			str_repeat('\])*', $this->nested_brackets_depth);
	
		$this->nested_url_parenthesis_re = 
			str_repeat('(?>[^()\s]+|\(', $this->nested_url_parenthesis_depth).
			str_repeat('(?>\)))*', $this->nested_url_parenthesis_depth);
		
		$this->escape_chars_re = '['.preg_quote($this->escape_chars).']';
		
		# Sort document, block, and span gamut in ascendent priority order.
		asort($this->document_gamut);
		asort($this->block_gamut);
		asort($this->span_gamut);
	}


	# Internal hashes used during transformation.
	var $urls = array();
	var $titles = array();
	var $html_hashes = array();
	
	# Status flag to avoid invalid nesting.
	var $in_anchor = false;
	
	
	function setup() {
	#
	# Called before the transformation process starts to setup parser 
	# states.
	#
		# Clear global hashes.
		$this->urls = $this->predef_urls;
		$this->titles = $this->predef_titles;
		$this->html_hashes = array();
		
		$in_anchor = false;
	}
	
	function teardown() {
	#
	# Called after the transformation process to clear any variable 
	# which may be taking up memory unnecessarly.
	#
		$this->urls = array();
		$this->titles = array();
		$this->html_hashes = array();
	}


	function transform($text) {
	#
	# Main function. Performs some preprocessing on the input text
	# and pass it through the document gamut.
	#
		$this->setup();
	
		# Remove UTF-8 BOM and marker character in input, if present.
		$text = preg_replace('{^\xEF\xBB\xBF|\x1A}', '', $text);

		# Standardize line endings:
		#   DOS to Unix and Mac to Unix
		$text = preg_replace('{\r\n?}', "\n", $text);

		# Make sure $text ends with a couple of newlines:
		$text .= "\n\n";

		# Convert all tabs to spaces.
		$text = $this->detab($text);

		# Turn block-level HTML blocks into hash entries
		$text = $this->hashHTMLBlocks($text);

		# Strip any lines consisting only of spaces and tabs.
		# This makes subsequent regexen easier to write, because we can
		# match consecutive blank lines with /\n+/ instead of something
		# contorted like /[ ]*\n+/ .
		$text = preg_replace('/^[ ]+$/m', '', $text);

		# Run document gamut methods.
		foreach ($this->document_gamut as $method => $priority) {
			$text = $this->$method($text);
		}
		
		$this->teardown();

		return $text . "\n";
	}
	
	var $document_gamut = array(
		# Strip link definitions, store in hashes.
		"stripLinkDefinitions" => 20,
		
		"runBasicBlockGamut"   => 30,
		);


	function stripLinkDefinitions($text) {
	#
	# Strips link definitions from text, stores the URLs and titles in
	# hash references.
	#
		$less_than_tab = $this->tab_width - 1;

		# Link defs are in the form: ^[id]: url "optional title"
		$text = preg_replace_callback('{
							^[ ]{0,'.$less_than_tab.'}\[(.+)\][ ]?:	# id = $1
							  [ ]*
							  \n?				# maybe *one* newline
							  [ ]*
							(?:
							  <(.+?)>			# url = $2
							|
							  (\S+?)			# url = $3
							)
							  [ ]*
							  \n?				# maybe one newline
							  [ ]*
							(?:
								(?<=\s)			# lookbehind for whitespace
								["(]
								(.*?)			# title = $4
								[")]
								[ ]*
							)?	# title is optional
							(?:\n+|\Z)
			}xm',
			array(&$this, '_stripLinkDefinitions_callback'),
			$text);
		return $text;
	}
	function _stripLinkDefinitions_callback($matches) {
		$link_id = strtolower($matches[1]);
		$url = $matches[2] == '' ? $matches[3] : $matches[2];
		$this->urls[$link_id] = $url;
		$this->titles[$link_id] =& $matches[4];
		return ''; # String that will replace the block
	}


	function hashHTMLBlocks($text) {
		if ($this->no_markup)  return $text;

		$less_than_tab = $this->tab_width - 1;

		# Hashify HTML blocks:
		# We only want to do this for block-level HTML tags, such as headers,
		# lists, and tables. That's because we still want to wrap <p>s around
		# "paragraphs" that are wrapped in non-block-level tags, such as anchors,
		# phrase emphasis, and spans. The list of tags we're looking for is
		# hard-coded:
		#
		# *  List "a" is made of tags which can be both inline or block-level.
		#    These will be treated block-level when the start tag is alone on 
		#    its line, otherwise they're not matched here and will be taken as 
		#    inline later.
		# *  List "b" is made of tags which are always block-level;
		#
		$block_tags_a_re = 'ins|del';
		$block_tags_b_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|'.
						   'script|noscript|form|fieldset|iframe|math';

		# Regular expression for the content of a block tag.
		$nested_tags_level = 4;
		$attr = '
			(?>				# optional tag attributes
			  \s			# starts with whitespace
			  (?>
				[^>"/]+		# text outside quotes
			  |
				/+(?!>)		# slash not followed by ">"
			  |
				"[^"]*"		# text inside double quotes (tolerate ">")
			  |
				\'[^\']*\'	# text inside single quotes (tolerate ">")
			  )*
			)?	
			';
		$content =
			str_repeat('
				(?>
				  [^<]+			# content without tag
				|
				  <\2			# nested opening tag
					'.$attr.'	# attributes
					(?>
					  />
					|
					  >', $nested_tags_level).	# end of opening tag
					  '.*?'.					# last level nested tag content
			str_repeat('
					  </\2\s*>	# closing nested tag
					)
				  |				
					<(?!/\2\s*>	# other tags with a different name
				  )
				)*',
				$nested_tags_level);
		$content2 = str_replace('\2', '\3', $content);

		# First, look for nested blocks, e.g.:
		# 	<div>
		# 		<div>
		# 		tags for inner block must be indented.
		# 		</div>
		# 	</div>
		#
		# The outermost tags must start at the left margin for this to match, and
		# the inner nested divs must be indented.
		# We need to do this before the next, more liberal match, because the next
		# match will start at the first `<div>` and stop at the first `</div>`.
		$text = preg_replace_callback('{(?>
			(?>
				(?<=\n\n)		# Starting after a blank line
				|				# or
				\A\n?			# the beginning of the doc
			)
			(						# save in $1

			  # Match from `\n<tag>` to `</tag>\n`, handling nested tags 
			  # in between.
					
						[ ]{0,'.$less_than_tab.'}
						<('.$block_tags_b_re.')# start tag = $2
						'.$attr.'>			# attributes followed by > and \n
						'.$content.'		# content, support nesting
						</\2>				# the matching end tag
						[ ]*				# trailing spaces/tabs
						(?=\n+|\Z)	# followed by a newline or end of document

			| # Special version for tags of group a.

						[ ]{0,'.$less_than_tab.'}
						<('.$block_tags_a_re.')# start tag = $3
						'.$attr.'>[ ]*\n	# attributes followed by >
						'.$content2.'		# content, support nesting
						</\3>				# the matching end tag
						[ ]*				# trailing spaces/tabs
						(?=\n+|\Z)	# followed by a newline or end of document
					
			| # Special case just for <hr />. It was easier to make a special 
			  # case than to make the other regex more complicated.
			
						[ ]{0,'.$less_than_tab.'}
						<(hr)				# start tag = $2
						'.$attr.'			# attributes
						/?>					# the matching end tag
						[ ]*
						(?=\n{2,}|\Z)		# followed by a blank line or end of document
			
			| # Special case for standalone HTML comments:
			
					[ ]{0,'.$less_than_tab.'}
					(?s:
						<!-- .*? -->
					)
					[ ]*
					(?=\n{2,}|\Z)		# followed by a blank line or end of document
			
			| # PHP and ASP-style processor instructions (<? and <%)
			
					[ ]{0,'.$less_than_tab.'}
					(?s:
						<([?%])			# $2
						.*?
						\2>
					)
					[ ]*
					(?=\n{2,}|\Z)		# followed by a blank line or end of document
					
			)
			)}Sxmi',
			array(&$this, '_hashHTMLBlocks_callback'),
			$text);

		return $text;
	}
	function _hashHTMLBlocks_callback($matches) {
		$text = $matches[1];
		$key  = $this->hashBlock($text);
		return "\n\n$key\n\n";
	}
	
	
	function hashPart($text, $boundary = 'X') {
	#
	# Called whenever a tag must be hashed when a function insert an atomic 
	# element in the text stream. Passing $text to through this function gives
	# a unique text-token which will be reverted back when calling unhash.
	#
	# The $boundary argument specify what character should be used to surround
	# the token. By convension, "B" is used for block elements that needs not
	# to be wrapped into paragraph tags at the end, ":" is used for elements
	# that are word separators and "X" is used in the general case.
	#
		# Swap back any tag hash found in $text so we do not have to `unhash`
		# multiple times at the end.
		$text = $this->unhash($text);
		
		# Then hash the block.
		static $i = 0;
		$key = "$boundary\x1A" . ++$i . $boundary;
		$this->html_hashes[$key] = $text;
		return $key; # String that will replace the tag.
	}


	function hashBlock($text) {
	#
	# Shortcut function for hashPart with block-level boundaries.
	#
		return $this->hashPart($text, 'B');
	}


	var $block_gamut = array(
	#
	# These are all the transformations that form block-level
	# tags like paragraphs, headers, and list items.
	#
		"doHeaders"         => 10,
		"doHorizontalRules" => 20,
		
		"doLists"           => 40,
		"doCodeBlocks"      => 50,
		"doBlockQuotes"     => 60,
		);

	function runBlockGamut($text) {
	#
	# Run block gamut tranformations.
	#
		# We need to escape raw HTML in Markdown source before doing anything 
		# else. This need to be done for each block, and not only at the 
		# begining in the Markdown function since hashed blocks can be part of
		# list items and could have been indented. Indented blocks would have 
		# been seen as a code block in a previous pass of hashHTMLBlocks.
		$text = $this->hashHTMLBlocks($text);
		
		return $this->runBasicBlockGamut($text);
	}
	
	function runBasicBlockGamut($text) {
	#
	# Run block gamut tranformations, without hashing HTML blocks. This is 
	# useful when HTML blocks are known to be already hashed, like in the first
	# whole-document pass.
	#
		foreach ($this->block_gamut as $method => $priority) {
			$text = $this->$method($text);
		}
		
		# Finally form paragraph and restore hashed blocks.
		$text = $this->formParagraphs($text);

		return $text;
	}
	
	
	function doHorizontalRules($text) {
		# Do Horizontal Rules:
		return preg_replace(
			'{
				^[ ]{0,3}	# Leading space
				([-*_])		# $1: First marker
				(?>			# Repeated marker group
					[ ]{0,2}	# Zero, one, or two spaces.
					\1			# Marker character
				){2,}		# Group repeated at least twice
				[ ]*		# Tailing spaces
				$			# End of line.
			}mx',
			"\n".$this->hashBlock("<hr$this->empty_element_suffix")."\n", 
			$text);
	}


	var $span_gamut = array(
	#
	# These are all the transformations that occur *within* block-level
	# tags like paragraphs, headers, and list items.
	#
		# Process character escapes, code spans, and inline HTML
		# in one shot.
		"parseSpan"           => -30,

		# Process anchor and image tags. Images must come first,
		# because ![foo][f] looks like an anchor.
		"doImages"            =>  10,
		"doAnchors"           =>  20,
		
		# Make links out of things like `<http://example.com/>`
		# Must come after doAnchors, because you can use < and >
		# delimiters in inline links like [this](<url>).
		"doAutoLinks"         =>  30,
		"encodeAmpsAndAngles" =>  40,

		"doItalicsAndBold"    =>  50,
		"doHardBreaks"        =>  60,
		);

	function runSpanGamut($text) {
	#
	# Run span gamut tranformations.
	#
		foreach ($this->span_gamut as $method => $priority) {
			$text = $this->$method($text);
		}

		return $text;
	}
	
	
	function doHardBreaks($text) {
		# Do hard breaks:
		return preg_replace_callback('/ {2,}\n/', 
			array(&$this, '_doHardBreaks_callback'), $text);
	}
	function _doHardBreaks_callback($matches) {
		return $this->hashPart("<br$this->empty_element_suffix\n");
	}


	function doAnchors($text) {
	#
	# Turn Markdown link shortcuts into XHTML <a> tags.
	#
		if ($this->in_anchor) return $text;
		$this->in_anchor = true;
		
		#
		# First, handle reference-style links: [link text] [id]
		#
		$text = preg_replace_callback('{
			(					# wrap whole match in $1
			  \[
				('.$this->nested_brackets_re.')	# link text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]
			)
			}xs',
			array(&$this, '_doAnchors_reference_callback'), $text);

		#
		# Next, inline-style links: [link text](url "optional title")
		#
		$text = preg_replace_callback('{
			(				# wrap whole match in $1
			  \[
				('.$this->nested_brackets_re.')	# link text = $2
			  \]
			  \(			# literal paren
				[ \n]*
				(?:
					<(.+?)>	# href = $3
				|
					('.$this->nested_url_parenthesis_re.')	# href = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# Title = $7
				  \6		# matching quote
				  [ \n]*	# ignore any spaces/tabs between closing quote and )
				)?			# title is optional
			  \)
			)
			}xs',
			array(&$this, '_doAnchors_inline_callback'), $text);

		#
		# Last, handle reference-style shortcuts: [link text]
		# These must come last in case you've also got [link text][1]
		# or [link text](/foo)
		#
		$text = preg_replace_callback('{
			(					# wrap whole match in $1
			  \[
				([^\[\]]+)		# link text = $2; can\'t contain [ or ]
			  \]
			)
			}xs',
			array(&$this, '_doAnchors_reference_callback'), $text);

		$this->in_anchor = false;
		return $text;
	}
	function _doAnchors_reference_callback($matches) {
		$whole_match =  $matches[1];
		$link_text   =  $matches[2];
		$link_id     =& $matches[3];

		if ($link_id == "") {
			# for shortcut links like [this][] or [this].
			$link_id = $link_text;
		}
		
		# lower-case and turn embedded newlines into spaces
		$link_id = strtolower($link_id);
		$link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

		if (isset($this->urls[$link_id])) {
			$url = $this->urls[$link_id];
			$url = $this->encodeAttribute($url);
			
			$result = "<a href=\"$url\"";
			if ( isset( $this->titles[$link_id] ) ) {
				$title = $this->titles[$link_id];
				$title = $this->encodeAttribute($title);
				$result .=  " title=\"$title\"";
			}
		
			$link_text = $this->runSpanGamut($link_text);
			$result .= ">$link_text</a>";
			$result = $this->hashPart($result);
		}
		else {
			$result = $whole_match;
		}
		return $result;
	}
	function _doAnchors_inline_callback($matches) {
		$whole_match	=  $matches[1];
		$link_text		=  $this->runSpanGamut($matches[2]);
		$url			=  $matches[3] == '' ? $matches[4] : $matches[3];
		$title			=& $matches[7];

		$url = $this->encodeAttribute($url);

		$result = "<a href=\"$url\"";
		if (isset($title)) {
			$title = $this->encodeAttribute($title);
			$result .=  " title=\"$title\"";
		}
		
		$link_text = $this->runSpanGamut($link_text);
		$result .= ">$link_text</a>";

		return $this->hashPart($result);
	}


	function doImages($text) {
	#
	# Turn Markdown image shortcuts into <img> tags.
	#
		#
		# First, handle reference-style labeled images: ![alt text][id]
		#
		$text = preg_replace_callback('{
			(				# wrap whole match in $1
			  !\[
				('.$this->nested_brackets_re.')		# alt text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]

			)
			}xs', 
			array(&$this, '_doImages_reference_callback'), $text);

		#
		# Next, handle inline images:  ![alt text](url "optional title")
		# Don't forget: encode * and _
		#
		$text = preg_replace_callback('{
			(				# wrap whole match in $1
			  !\[
				('.$this->nested_brackets_re.')		# alt text = $2
			  \]
			  \s?			# One optional whitespace character
			  \(			# literal paren
				[ \n]*
				(?:
					<(\S*)>	# src url = $3
				|
					('.$this->nested_url_parenthesis_re.')	# src url = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# title = $7
				  \6		# matching quote
				  [ \n]*
				)?			# title is optional
			  \)
			)
			}xs',
			array(&$this, '_doImages_inline_callback'), $text);

		return $text;
	}
	function _doImages_reference_callback($matches) {
		$whole_match = $matches[1];
		$alt_text    = $matches[2];
		$link_id     = strtolower($matches[3]);

		if ($link_id == "") {
			$link_id = strtolower($alt_text); # for shortcut links like ![this][].
		}

		$alt_text = $this->encodeAttribute($alt_text);
		if (isset($this->urls[$link_id])) {
			$url = $this->encodeAttribute($this->urls[$link_id]);
			$result = "<img src=\"$url\" alt=\"$alt_text\"";
			if (isset($this->titles[$link_id])) {
				$title = $this->titles[$link_id];
				$title = $this->encodeAttribute($title);
				$result .=  " title=\"$title\"";
			}
			$result .= $this->empty_element_suffix;
			$result = $this->hashPart($result);
		}
		else {
			# If there's no such link ID, leave intact:
			$result = $whole_match;
		}

		return $result;
	}
	function _doImages_inline_callback($matches) {
		$whole_match	= $matches[1];
		$alt_text		= $matches[2];
		$url			= $matches[3] == '' ? $matches[4] : $matches[3];
		$title			=& $matches[7];

		$alt_text = $this->encodeAttribute($alt_text);
		$url = $this->encodeAttribute($url);
		$result = "<img src=\"$url\" alt=\"$alt_text\"";
		if (isset($title)) {
			$title = $this->encodeAttribute($title);
			$result .=  " title=\"$title\""; # $title already quoted
		}
		$result .= $this->empty_element_suffix;

		return $this->hashPart($result);
	}


	function doHeaders($text) {
		# Setext-style headers:
		#	  Header 1
		#	  ========
		#  
		#	  Header 2
		#	  --------
		#
		$text = preg_replace_callback('{ ^(.+?)[ ]*\n(=+|-+)[ ]*\n+ }mx',
			array(&$this, '_doHeaders_callback_setext'), $text);

		# atx-style headers:
		#	# Header 1
		#	## Header 2
		#	## Header 2 with closing hashes ##
		#	...
		#	###### Header 6
		#
		$text = preg_replace_callback('{
				^(\#{1,6})	# $1 = string of #\'s
				[ ]*
				(.+?)		# $2 = Header text
				[ ]*
				\#*			# optional closing #\'s (not counted)
				\n+
			}xm',
			array(&$this, '_doHeaders_callback_atx'), $text);

		return $text;
	}
	function _doHeaders_callback_setext($matches) {
		# Terrible hack to check we haven't found an empty list item.
		if ($matches[2] == '-' && preg_match('{^-(?: |$)}', $matches[1]))
			return $matches[0];
		
		$level = $matches[2]{0} == '=' ? 1 : 2;
		$block = "<h$level>".$this->runSpanGamut($matches[1])."</h$level>";
		return "\n" . $this->hashBlock($block) . "\n\n";
	}
	function _doHeaders_callback_atx($matches) {
		$level = strlen($matches[1]);
		$block = "<h$level>".$this->runSpanGamut($matches[2])."</h$level>";
		return "\n" . $this->hashBlock($block) . "\n\n";
	}


	function doLists($text) {
	#
	# Form HTML ordered (numbered) and unordered (bulleted) lists.
	#
		$less_than_tab = $this->tab_width - 1;

		# Re-usable patterns to match list item bullets and number markers:
		$marker_ul_re  = '[*+-]';
		$marker_ol_re  = '\d+[\.]';
		$marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";

		$markers_relist = array(
			$marker_ul_re => $marker_ol_re,
			$marker_ol_re => $marker_ul_re,
			);

		foreach ($markers_relist as $marker_re => $other_marker_re) {
			# Re-usable pattern to match any entirel ul or ol list:
			$whole_list_re = '
				(								# $1 = whole list
				  (								# $2
					([ ]{0,'.$less_than_tab.'})	# $3 = number of spaces
					('.$marker_re.')			# $4 = first list item marker
					[ ]+
				  )
				  (?s:.+?)
				  (								# $5
					  \z
					|
					  \n{2,}
					  (?=\S)
					  (?!						# Negative lookahead for another list item marker
						[ ]*
						'.$marker_re.'[ ]+
					  )
					|
					  (?=						# Lookahead for another kind of list
					    \n
						\3						# Must have the same indentation
						'.$other_marker_re.'[ ]+
					  )
				  )
				)
			'; // mx
			
			# We use a different prefix before nested lists than top-level lists.
			# See extended comment in _ProcessListItems().
		
			if ($this->list_level) {
				$text = preg_replace_callback('{
						^
						'.$whole_list_re.'
					}mx',
					array(&$this, '_doLists_callback'), $text);
			}