Parsedown: sub/superscript - php

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?
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

Append Superscript and Tilde in $InlineTypes:
protected $InlineTypes = array(
'!' => array('Image'),
'&' => array('SpecialCharacter'),
'*' => array('Emphasis'),
':' => array('Url'),
'<' => array('UrlTag', 'EmailTag', 'Markup'),
'[' => array('Link'),
'_' => array('Emphasis'),
'`' => array('Code'),
'~' => array('Tilde'),
'^' => array('Superscript'),
'\\' => array('EscapeSequence'),
);
Define methods inlineSuperscript. It should look pretty much like inlineStrikethrough:
protected function inlineSuperscript($Excerpt)
{
if (preg_match('/^\^(.+?)\^/', $Excerpt['text'], $matches))
{
return array(
'extent' => strlen($matches[0]),
'element' => array(
'name' => 'sup',
'handler' => array(
'function' => 'lineElements',
'argument' => $matches[1],
'destination' => 'elements',
)
),
);
}
}
Define methods inlineTilde and delete method inlineStrikethrough. It should look pretty much like inlineEmphasis:
protected function inlineTilde($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',
)
),
);
}
Add the new symbol to $inlineMarkerList:
protected $inlineMarkerList = '!*_&[:<`~\\^';