Regex Named Capture Groups — Every Syntax

Define syntax by engine

Engine	Define	Backreference
JavaScript (ES2018)	(?<year>\d{4})	\k<year>
Python	(?P<year>\d{4})	(?P=year)
Java	(?<year>\d{4})	\k<year>
PHP / PCRE	(?<year>...) or (?P<year>...)	(?P=year)
.NET	(?<year>\d{4})	\k<year>
Go (RE2)	(?P<year>\d{4})	none (no backrefs)

Read the value in your code

# Python
import re
m = re.search(r'(?P<year>\d{4})-(?P<month>\d{2})', '2026-09')
m.group('year')      # -> '2026'
m.groupdict()        # -> {'year': '2026', 'month': '09'}

// JavaScript
const m = '2026-09'.match(/(?<year>\d{4})-(?<month>\d{2})/);
m.groups.year;       // -> '2026'

Why bother with names?

Numeric groups break the moment you insert a new group earlier in the pattern — every index shifts. Named groups are stable, self-documenting, and let you build a dictionary of results in one call (groupdict() in Python, .groups in JS). For any regex you will revisit, names pay for themselves.

Portability tip

The (?<name>...) form is the widest-supported today. Python accepted only (?P<name>...) for years, so if you copy a pattern from Python docs into JavaScript, rewrite (?P<name>...) to (?<name>...) and (?P=name) to \k<name>.