Mastodawn

things that are much harder to describe accurately with a regex than you'd think, an incomplete list:

* floating point numbers
* IPv6 addresses
* IPv*4* addresses (depending on how you define them and how picky you are about the numeric ranges)
* ...

Email addresses.
URLs.
Phone numbers.

Dates and times (and how)
URLs and URIs (they contain some of the things already mentioned)

@ancoghlan @elithebearded @zwol at least there is official guidance on the latter now, so people have something to move *to* instead of ad-hoc implementations (many of which will be sub-par regexes) https://www.unicode.org/reports/tr58/