ReDoS Countermeasures

Ensure proper timeouts, input validations or other [Regular Expression Denial of Service](https://en.wikipedia.org/wiki/ReDoS) countermeasures are in place for each regex engine.

Note that [Wikipedia cites regexlib.com](https://en.wikipedia.org/wiki/ReDoS#Vulnerable_regexes_in_online_repositories) as persisting evil (malicious) regexes, i.e. http://regexlib.com/REDetails.aspx?regexp_id=1757

The issue names no files, tests, or entry points. Start by locating each regex engine and the paths that accept or process regular expressions, then determine how validation, timeouts, or other ReDoS protections should apply to each; done means every engine has an identified countermeasure.

Written by the indexing model from the issue text.