Atom feeds fail to sanitize output HTML

[GiovanH]

• I have read the Filing Issues and subsequent “How to Get Help” sections of the documentation.

• I have searched the issues (including closed ones) and believe that this is not a duplicate.

• Pelican version: 4.9

Issue

Atom feeds require HTML in the summary to be sanitized:

• https://validator.w3.org/feed/docs/warning/SecurityRiskAttr.html
• https://validator.w3.org/feed/docs/warning/NotHtml.html

However, the current atom writer does not do this: https://github.com/getpelican/pelican/blob/master/pelican/writers.py#L68-L78

In addition, there is HTML that is valid for a browser, but not valid for atom feeds, like custom-named tags.

The HTML content cannot be used naively as the feed body. Additional sanitization is required here.

Example of issues

https://validator.w3.org/feed/check.cgi?url=https://blog.giovanh.com/feeds/atom.xml