Suggestion for matching spaces in regular expressions

[Mark-L6n]

Looking at regular expressions in the source code, I see the following for optional spaces: r' *'.
An issue for using a space character instead of a character class for matching spaces is that there are a variety of code points used for spaces in UTF8/Unicode, see https://www.compart.com/en/unicode/category/Zs
To make this more robust, the re module provides the character class \s for spaces, but this also includes the character codes for carriage returns.
The regex module provides a \h character class, "horizontal spaces", which solves this problem, for ex regex.search(r'^\h*...', str)
In my experience, regex has otherwise performed the same as re, not requiring any code changes.

[lepture]

I'd like to keep mistune dependency free.