diff --git a/kernel/parsedownextra.class.php b/kernel/parsedownextra.class.php
new file mode 100644
index 00000000..be6966d2
--- /dev/null
+++ b/kernel/parsedownextra.class.php
@@ -0,0 +1,526 @@
+BlockTypes[':'] []= 'DefinitionList';
+ $this->BlockTypes['*'] []= 'Abbreviation';
+
+ # identify footnote definitions before reference definitions
+ array_unshift($this->BlockTypes['['], 'Footnote');
+
+ # identify footnote markers before before links
+ array_unshift($this->InlineTypes['['], 'FootnoteMarker');
+ }
+
+ #
+ # ~
+
+ function text($text)
+ {
+ $markup = parent::text($text);
+
+ # merge consecutive dl elements
+
+ $markup = preg_replace('/<\/dl>\s+
\s+/', '', $markup);
+
+ # add footnotes
+
+ if (isset($this->DefinitionData['Footnote']))
+ {
+ $Element = $this->buildFootnoteElement();
+
+ $markup .= "\n" . $this->element($Element);
+ }
+
+ return $markup;
+ }
+
+ #
+ # Blocks
+ #
+
+ #
+ # Abbreviation
+
+ protected function blockAbbreviation($Line)
+ {
+ if (preg_match('/^\*\[(.+?)\]:[ ]*(.+?)[ ]*$/', $Line['text'], $matches))
+ {
+ $this->DefinitionData['Abbreviation'][$matches[1]] = $matches[2];
+
+ $Block = array(
+ 'hidden' => true,
+ );
+
+ return $Block;
+ }
+ }
+
+ #
+ # Footnote
+
+ protected function blockFootnote($Line)
+ {
+ if (preg_match('/^\[\^(.+?)\]:[ ]?(.*)$/', $Line['text'], $matches))
+ {
+ $Block = array(
+ 'label' => $matches[1],
+ 'text' => $matches[2],
+ 'hidden' => true,
+ );
+
+ return $Block;
+ }
+ }
+
+ protected function blockFootnoteContinue($Line, $Block)
+ {
+ if ($Line['text'][0] === '[' and preg_match('/^\[\^(.+?)\]:/', $Line['text']))
+ {
+ return;
+ }
+
+ if (isset($Block['interrupted']))
+ {
+ if ($Line['indent'] >= 4)
+ {
+ $Block['text'] .= "\n\n" . $Line['text'];
+
+ return $Block;
+ }
+ }
+ else
+ {
+ $Block['text'] .= "\n" . $Line['text'];
+
+ return $Block;
+ }
+ }
+
+ protected function blockFootnoteComplete($Block)
+ {
+ $this->DefinitionData['Footnote'][$Block['label']] = array(
+ 'text' => $Block['text'],
+ 'count' => null,
+ 'number' => null,
+ );
+
+ return $Block;
+ }
+
+ #
+ # Definition List
+
+ protected function blockDefinitionList($Line, $Block)
+ {
+ if ( ! isset($Block) or isset($Block['type']))
+ {
+ return;
+ }
+
+ $Element = array(
+ 'name' => 'dl',
+ 'handler' => 'elements',
+ 'text' => array(),
+ );
+
+ $terms = explode("\n", $Block['element']['text']);
+
+ foreach ($terms as $term)
+ {
+ $Element['text'] []= array(
+ 'name' => 'dt',
+ 'handler' => 'line',
+ 'text' => $term,
+ );
+ }
+
+ $Block['element'] = $Element;
+
+ $Block = $this->addDdElement($Line, $Block);
+
+ return $Block;
+ }
+
+ protected function blockDefinitionListContinue($Line, array $Block)
+ {
+ if ($Line['text'][0] === ':')
+ {
+ $Block = $this->addDdElement($Line, $Block);
+
+ return $Block;
+ }
+ else
+ {
+ if (isset($Block['interrupted']) and $Line['indent'] === 0)
+ {
+ return;
+ }
+
+ if (isset($Block['interrupted']))
+ {
+ $Block['dd']['handler'] = 'text';
+ $Block['dd']['text'] .= "\n\n";
+
+ unset($Block['interrupted']);
+ }
+
+ $text = substr($Line['body'], min($Line['indent'], 4));
+
+ $Block['dd']['text'] .= "\n" . $text;
+
+ return $Block;
+ }
+ }
+
+ #
+ # Header
+
+ protected function blockHeader($Line)
+ {
+ $Block = parent::blockHeader($Line);
+
+ if (preg_match('/[ #]*{('.$this->regexAttribute.'+)}[ ]*$/', $Block['element']['text'], $matches, PREG_OFFSET_CAPTURE))
+ {
+ $attributeString = $matches[1][0];
+
+ $Block['element']['attributes'] = $this->parseAttributeData($attributeString);
+
+ $Block['element']['text'] = substr($Block['element']['text'], 0, $matches[0][1]);
+ }
+
+ return $Block;
+ }
+
+ #
+ # Markup
+
+ protected function blockMarkupComplete($Block)
+ {
+ if ( ! isset($Block['void']))
+ {
+ $Block['markup'] = $this->processTag($Block['markup']);
+ }
+
+ return $Block;
+ }
+
+ #
+ # Setext
+
+ protected function blockSetextHeader($Line, array $Block = null)
+ {
+ $Block = parent::blockSetextHeader($Line, $Block);
+
+ if (preg_match('/[ ]*{('.$this->regexAttribute.'+)}[ ]*$/', $Block['element']['text'], $matches, PREG_OFFSET_CAPTURE))
+ {
+ $attributeString = $matches[1][0];
+
+ $Block['element']['attributes'] = $this->parseAttributeData($attributeString);
+
+ $Block['element']['text'] = substr($Block['element']['text'], 0, $matches[0][1]);
+ }
+
+ return $Block;
+ }
+
+ #
+ # Inline Elements
+ #
+
+ #
+ # Footnote Marker
+
+ protected function inlineFootnoteMarker($Excerpt)
+ {
+ if (preg_match('/^\[\^(.+?)\]/', $Excerpt['text'], $matches))
+ {
+ $name = $matches[1];
+
+ if ( ! isset($this->DefinitionData['Footnote'][$name]))
+ {
+ return;
+ }
+
+ $this->DefinitionData['Footnote'][$name]['count'] ++;
+
+ if ( ! isset($this->DefinitionData['Footnote'][$name]['number']))
+ {
+ $this->DefinitionData['Footnote'][$name]['number'] = ++ $this->footnoteCount; # ยป &
+ }
+
+ $Element = array(
+ 'name' => 'sup',
+ 'attributes' => array('id' => 'fnref'.$this->DefinitionData['Footnote'][$name]['count'].':'.$name),
+ 'handler' => 'element',
+ 'text' => array(
+ 'name' => 'a',
+ 'attributes' => array('href' => '#fn:'.$name, 'class' => 'footnote-ref'),
+ 'text' => $this->DefinitionData['Footnote'][$name]['number'],
+ ),
+ );
+
+ return array(
+ 'extent' => strlen($matches[0]),
+ 'element' => $Element,
+ );
+ }
+ }
+
+ private $footnoteCount = 0;
+
+ #
+ # Link
+
+ protected function inlineLink($Excerpt)
+ {
+ $Link = parent::inlineLink($Excerpt);
+
+ $remainder = substr($Excerpt['text'], $Link['extent']);
+
+ if (preg_match('/^[ ]*{('.$this->regexAttribute.'+)}/', $remainder, $matches))
+ {
+ $Link['element']['attributes'] += $this->parseAttributeData($matches[1]);
+
+ $Link['extent'] += strlen($matches[0]);
+ }
+
+ return $Link;
+ }
+
+ #
+ # ~
+ #
+
+ protected function unmarkedText($text)
+ {
+ $text = parent::unmarkedText($text);
+
+ if (isset($this->DefinitionData['Abbreviation']))
+ {
+ foreach ($this->DefinitionData['Abbreviation'] as $abbreviation => $meaning)
+ {
+ $pattern = '/\b'.preg_quote($abbreviation, '/').'\b/';
+
+ $text = preg_replace($pattern, ''.$abbreviation.'', $text);
+ }
+ }
+
+ return $text;
+ }
+
+ #
+ # Util Methods
+ #
+
+ protected function addDdElement(array $Line, array $Block)
+ {
+ $text = substr($Line['text'], 1);
+ $text = trim($text);
+
+ unset($Block['dd']);
+
+ $Block['dd'] = array(
+ 'name' => 'dd',
+ 'handler' => 'line',
+ 'text' => $text,
+ );
+
+ if (isset($Block['interrupted']))
+ {
+ $Block['dd']['handler'] = 'text';
+
+ unset($Block['interrupted']);
+ }
+
+ $Block['element']['text'] []= & $Block['dd'];
+
+ return $Block;
+ }
+
+ protected function buildFootnoteElement()
+ {
+ $Element = array(
+ 'name' => 'div',
+ 'attributes' => array('class' => 'footnotes'),
+ 'handler' => 'elements',
+ 'text' => array(
+ array(
+ 'name' => 'hr',
+ ),
+ array(
+ 'name' => 'ol',
+ 'handler' => 'elements',
+ 'text' => array(),
+ ),
+ ),
+ );
+
+ uasort($this->DefinitionData['Footnote'], 'self::sortFootnotes');
+
+ foreach ($this->DefinitionData['Footnote'] as $definitionId => $DefinitionData)
+ {
+ if ( ! isset($DefinitionData['number']))
+ {
+ continue;
+ }
+
+ $text = $DefinitionData['text'];
+
+ $text = parent::text($text);
+
+ $numbers = range(1, $DefinitionData['count']);
+
+ $backLinksMarkup = '';
+
+ foreach ($numbers as $number)
+ {
+ $backLinksMarkup .= ' ';
+ }
+
+ $backLinksMarkup = substr($backLinksMarkup, 1);
+
+ if (substr($text, - 4) === '')
+ {
+ $backLinksMarkup = ' '.$backLinksMarkup;
+
+ $text = substr_replace($text, $backLinksMarkup.'', - 4);
+ }
+ else
+ {
+ $text .= "\n".''.$backLinksMarkup.'
';
+ }
+
+ $Element['text'][1]['text'] []= array(
+ 'name' => 'li',
+ 'attributes' => array('id' => 'fn:'.$definitionId),
+ 'text' => "\n".$text."\n",
+ );
+ }
+
+ return $Element;
+ }
+
+ # ~
+
+ protected function parseAttributeData($attributeString)
+ {
+ $Data = array();
+
+ $attributes = preg_split('/[ ]+/', $attributeString, - 1, PREG_SPLIT_NO_EMPTY);
+
+ foreach ($attributes as $attribute)
+ {
+ if ($attribute[0] === '#')
+ {
+ $Data['id'] = substr($attribute, 1);
+ }
+ else # "."
+ {
+ $classes []= substr($attribute, 1);
+ }
+ }
+
+ if (isset($classes))
+ {
+ $Data['class'] = implode(' ', $classes);
+ }
+
+ return $Data;
+ }
+
+ # ~
+
+ protected function processTag($elementMarkup) # recursive
+ {
+ # http://stackoverflow.com/q/1148928/200145
+ libxml_use_internal_errors(true);
+
+ $DOMDocument = new DOMDocument;
+
+ # http://stackoverflow.com/q/11309194/200145
+ $elementMarkup = mb_convert_encoding($elementMarkup, 'HTML-ENTITIES', 'UTF-8');
+
+ # http://stackoverflow.com/q/4879946/200145
+ $DOMDocument->loadHTML($elementMarkup);
+ $DOMDocument->removeChild($DOMDocument->doctype);
+ $DOMDocument->replaceChild($DOMDocument->firstChild->firstChild->firstChild, $DOMDocument->firstChild);
+
+ $elementText = '';
+
+ if ($DOMDocument->documentElement->getAttribute('markdown') === '1')
+ {
+ foreach ($DOMDocument->documentElement->childNodes as $Node)
+ {
+ $elementText .= $DOMDocument->saveHTML($Node);
+ }
+
+ $DOMDocument->documentElement->removeAttribute('markdown');
+
+ $elementText = "\n".$this->text($elementText)."\n";
+ }
+ else
+ {
+ foreach ($DOMDocument->documentElement->childNodes as $Node)
+ {
+ $nodeMarkup = $DOMDocument->saveHTML($Node);
+
+ if ($Node instanceof DOMElement and ! in_array($Node->nodeName, $this->textLevelElements))
+ {
+ $elementText .= $this->processTag($nodeMarkup);
+ }
+ else
+ {
+ $elementText .= $nodeMarkup;
+ }
+ }
+ }
+
+ # because we don't want for markup to get encoded
+ $DOMDocument->documentElement->nodeValue = 'placeholder\x1A';
+
+ $markup = $DOMDocument->saveHTML($DOMDocument->documentElement);
+ $markup = str_replace('placeholder\x1A', $elementText, $markup);
+
+ return $markup;
+ }
+
+ # ~
+
+ protected function sortFootnotes($A, $B) # callback
+ {
+ return $A['number'] - $B['number'];
+ }
+
+ #
+ # Fields
+ #
+
+ protected $regexAttribute = '(?:[#.][-\w]+[ ]*)';
+}