Parsedown: sub/superscript

Question

The current version of Parsedown 1.8.0-beta-5 doesn't have a builtin syntax for sub/superscript. Although CommonMark doesn't specify such syntax, several other lightweight markup languages (ex: Parsedown Extreme, Textile) use a syntax similar to the following:

in: 19^th^  
out: 19<sup>th</sup>

in: H~2~O  
out: H<sub>2</sub>O

Question
What steps should be taken in order to modify Parsedown.php file and include such syntax?

 

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Note: This issue has already come up other times (Parsedown, add sub/superscript). However, there is still no step-by-step guide explaining what modifications should be done in Parsedown.php file in order to achieve that.

Answer 1

1. Append Superscript and Tilde in $InlineTypes:

   protected $InlineTypes = array(
       '!' => array('Image'),
       '&' => array('SpecialCharacter'),
       '*' => array('Emphasis'),
       ':' => array('Url'),
       '<' => array('UrlTag', 'EmailTag', 'Markup'),
       '[' => array('Link'),
       '_' => array('Emphasis'),
       '`' => array('Code'),
       '~' => array('Tilde'),
       '^' => array('Superscript'),
       '\\' => array('EscapeSequence'),
   );
   

2. Define methods inlineSuperscript. It should look pretty much like inlineStrikethrough:

   protected function inlineSuperscript($Excerpt)
   {
       if (preg_match('/^\^(.+?)\^/', $Excerpt['text'], $matches))
       {
           return array(
               'extent' => strlen($matches[0]),
               'element' => array(
                   'name' => 'sup',
                   'handler' => array(
                       'function' => 'lineElements',
                       'argument' => $matches[1],
                       'destination' => 'elements',
                   )
               ),
           );
       }
   }
   

3. Define methods inlineTilde and delete method inlineStrikethrough. It should look pretty much like inlineEmphasis:

   protected function inlineTilde($Excerpt)
   {
       if ( ! isset($Excerpt['text'][1]))
       {
           return;
       }
   
       $marker = $Excerpt['text'][0];
   
       if ($Excerpt['text'][1] === $marker and preg_match('/^~~(?=\S)(.+?)(?<=\S)~~/', $Excerpt['text'], $matches))
       {
           $emphasis = 'del';
       }
       elseif (preg_match('/^~(?=\S)(.+?)(?<=\S)~/', $Excerpt['text'], $matches))
       {
           $emphasis = 'sub';
       }
       else
       {
           return;
       }
   
       return array(
           'extent' => strlen($matches[0]),
           'element' => array(
               'name' => $emphasis,
               'handler' => array(
                   'function' => 'lineElements',
                   'argument' => $matches[1],
                   'destination' => 'elements',
               )
           ),
       );
   }
   

4. Add the new symbol to $inlineMarkerList:

   protected $inlineMarkerList = '!*_&[:<`~\\^';