# MMark Limitations

NOTE: This page only applies to neuron version 0.4 or below, which used the mmark Markdown parser. Beginning from neuron version 0.5, however, Pandoc (via commonmark-hs) is used to represent Markdown, where these limitations do not apply. This page is left here for legacy reference. See issue #137 for details.

Zettel Markdown format is limited in a few ways owing to the strict parsing nature of mmark, the parser library used by neuron.

Notably, URI references must respect RFC 3986. Quotting mmark’s README:

All URI references (in links, images, autolinks, etc.) are parsed as per RFC 3986, no support for escaping or support for entity and numeric character references is provided. In addition to that, when a URI reference in not enclosed with < and >, then closing parenthesis character ) is not considered part of URI (use <uri> syntax if you want a closing parenthesis as part of a URI).