Incomplete list of empty HTML tags leads to invalid HTML

[nicbou]

I have made an extension to replace <img> tags with <figure> and <picture> tags. This is the expected output:

<picture>
    <source ...>
    <img ...>
</picture>

Unfortunately, the <source> element has a closing </source> tag. That's invalid HTML. I traced it to this line in the code. The source element is missing from Python Markdown's internal list of empty elements.

The full list of empty elements includes:

<area>
<base>
<br>
<col>
<embed>
<hr>
<img>
<input>
<link>
<meta>
<param> (deprecated)
<source>
<track>
<wbr>

[nicbou]

Actually, why not use Python's native list of elements?

https://github.com/python/cpython/blob/main/Lib/xml/etree/ElementTree.py#L899