Extend PHP Fat-Free (F3) with MetaMarkdown. Setting a global 'meta' var that can be used later on.

metamarkdown.php

<?php
class MetaMarkdown extends Markdown {

  protected function meta($txt) {
    $pattern = '/^([A-Za-z]+)\:\s*\t*(.+)$/m';
    //$pattern = '/^(.*)\:(?\s*)(?\t*)(.+)(\r\n|\n)/';
    //echo $txt;
    $txt = preg_replace_callback(
      '/^([A-Za-z]+)\:\s*\t*(.+)$/m',
      function($expr) {
        F3::instance()->set('meta.'.strtolower($expr[1]),$expr[2]);
        return "";
      },
      $txt
    );
    return $txt;
  }

  function convert($txt) {
    $txt = $this->meta($txt);
    $txt=preg_replace_callback(
      '/(<code.*?>.+?<\/code>|'.
      '<[^>\n]+>|\([^\n\)]+\)|"[^"\n]+")|'.
      '\\\\(.)/s',
      function($expr) {
        // Process escaped characters
        return empty($expr[1])?$expr[2]:$expr[1];
      },
      $this->build(preg_replace('/\r\n|\r/',"\n",$txt))
    );
    return $this->snip($txt);
  }
}
?>

my-markdown.md

Title: Meta Markdown Gist Author: Nick Kempinski Date: April, 6 2014

Meta Markdown Gist

Once upon a time, there was Nick!

sample.php

<?php
    $file = F3::instance()->read('my-markdown.md');
    # Old Markdown
    $html = Markdown::instance()->convert($file);

    # Look for 'meta'
    var_dump(F3::instance()->get('meta'));
    # = NULL

    # New & Improved Markdown
    $meta_html = MetaMarkdown::instance()->convert($file);

    # $html == $meta_html
    # but now with added 'meta'
    var_dump(F3::instance()->get('meta'));
    # = { ["title"]=> string(18) "Meta Markdown Gist" ["author"]=> string(14) "Nick Kempinski" ["date"]=> string(13) "April, 6 2014" }
?>