CONTRIBUTING.md

How python vs rust regexes

• re.match searches at the beginning of a string
• re.search searches anywhere at the string
• pip has regex package used here
• regex::is_match has implicit .*? at the beginning and end of a pattern
• fancy-regex does not support branches during backtracking

When porting, be careful in tracking all regex usages. If re.is_match used, prepend the regular expression with ^.