XML



 XML  is a markup language syntax, similar to SGML, but with draconian error handling that tends to make it fragile in practice.

How to not
How to not use XML, use HTML instead:
 * If you're thinking of building something on/with XML, stop, and consider building on HTML instead. Beyond the obvious example of microformats, this lesson has been (re)learned many times across industries, e.g. 2021-06-26 One Enormous Step at a Time – Now JATS "… start with a HTML-compliant hierarchical structure, and add additional structure and data to it progressively – without needing to know anything about XML."

Fragile
See numerous cited examples and writeups at:
 * https://twitter.com/search?q=%22XML%20is%20fragile%22%20OR%20%22fragile%20XML%22&src=typed_query&f=live

Security Vulnerabilities
It is also susceptible to security vulnerabilities. See the description of the defusedxml Python library for a list of attacks.


 * XML is so hard to parse, Apple upped their amount of parsers from 4 to 6 to fix a vulnerability.