Parser capabilities

The package parses regex patterns and substitution strings. Syntax rules and validation depend on the selected flavor.

Flavor support

Both parser functions accept these flavors. The table lists parser flavors, not matching-engine versions.

Flavor	Exported value	String identifier
PCRE2	Flavors.PCRE2	pcre2
PCRE	Flavors.PCRE	pcre
JavaScript	Flavors.JAVASCRIPT	javascript
Python	Flavors.PYTHON	python
Go	Flavors.GOLANG	golang
Java	Flavors.JAVA	java
.NET	Flavors.DOTNET	dotnet
Rust	Flavors.RUST	rust
POSIX ERE	Flavors.POSIX_ERE	posix_ere
POSIX BRE	Flavors.POSIX_BRE	posix_bre

Syntax coverage

The parser recognizes these constructs when the selected flavor supports them:

• Capturing groups, named groups, and backreferences
• Alternation, quantifiers, atomic groups, and possessive quantifiers
• Lookaheads, lookbehinds, and flavor-specific width validation
• Subroutine calls, conditional expressions, verbs, and callouts
• Character classes, intersections, subtraction, and POSIX classes
• Inline modifiers, comments, anchors, and quoted literals
• Unicode escapes, Unicode properties, and flavor-specific Unicode modes
• Numeric, named, and special insertions in substitution strings

Output and metadata

• A typed token tree based on discriminated TypeScript unions
• Start and end positions for each token
• Typed error codes on invalid tokens
• Partial token output after a syntax error
• Parent, previous-token, related-token, and reference relationships
• Exact, minimum, and maximum match-width metadata
• Parser state for groups, flags, Unicode modes, and flavor features

Public helpers

• getFlavorFlagDefinition and validateFlags for flavor flags
• Type guards for groups and lookarounds
• getTokenMarker and resolveRepresentativeToken for editor highlighting
• getLineTerminatorCodePoints and getCharCode for character data
• isBacktrackingFlavor for engine classification

Scope

The package parses and validates syntax. It does not execute patterns, apply substitutions, lint style, or assess ReDoS risk.

Verify matching behavior in your target regex engine.

Related articlesParse a pattern with explicit options