# Disallowed Raw HTML (extension)

GFM enables the tagfilter extension, where the following HTML tags will be filtered when rendering HTML output:

  • <title>
  • <textarea>
  • <style>
  • <xmp>
  • <iframe>
  • <noembed>
  • <noframes>
  • <script>
  • <plaintext>

Filtering is done by replacing the leading < with the entity &lt;. These tags are chosen in particular as they change how HTML is interpreted in a way unique to them (i.e. nested HTML is interpreted differently), and this is usually undesireable in the context of other rendered Markdown content.
All other HTML tags are left untouched.

Example 653

Markdown HTML Demo
<strong> <title> <style> <em>

  <xmp> is disallowed.  <XMP> is also disallowed.

<p><strong> &lt;title> &lt;style> <em></p>
  &lt;xmp> is disallowed.  &lt;XMP> is also disallowed.