Improved submatch tracking by storing all group indices as a part of the state, which is viewed as a 'thread'

nfa.go

@@ -33,10 +33,11 @@ type State struct {
 	except                     []rune           // Only valid if allChars is true - match all characters _except_ the ones in this block. Useful for inverting character classes.
 	lookaroundRegex            string           // Only for lookaround states - Contents of the regex that the lookaround state holds
 	lookaroundNFA              *State           // Holds the NFA of the lookaroundRegex - if it exists
-	lookaroundNumCaptureGroups int              // Number of capturing groups if current node is a lookaround
+	lookaroundNumCaptureGroups int              // Number of capturing groups in lookaround regex if current node is a lookaround
 	groupBegin                 bool             // Whether or not the node starts a capturing group
 	groupEnd                   bool             // Whether or not the node ends a capturing group
 	groupNum                   int              // Which capturing group the node starts / ends
+	threadGroups               []Group          // Assuming that a state is part of a 'thread' in the matching process, this array stores the indices of capturing groups in the current thread. As matches are found for this state, its groups will be copied over.
 }
 
 // Clones the NFA starting from the given state.