DEELX Extended Syntax: Recursive Expression

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Recursive Expression (?R)

"Recursive expression" is to refer to another part of expression itself, not to refer to what is captured. If the part which is referred, contains the "recursive expression", this makes a recursion.

Remarks

"Recursive expression" is to refer to another part of expression itself, not to refer to what is captured. For example:

Expression	Equivalent1	Equivalent2	Matches
(\w)(?1)	(\w)(\w)		ab
(?1)(\w(?2))(\d)	(?1)(\w(\d))(\d)	(\w(\d))(\w(\d))(\d)	a1b23

If the part which is referred, contains the "recursive expression", this makes a recursion. For example:

Expression	Equivalent1	Equivalent1	Matches
(\w(?1)?)	(\w(\w(?1)?)?)	(\w+)	ghjk5......
\(([^()]|(?R))*\)	\(([^()]|\(([^()]|(?R))*\))*\)		(a * (c + 2))

Formats of recursive expression:

Format	Description
(?R)	Recursively refer to the whole expression.
(?R1), (?R2)	Recursively refer to certain group.
(?1), (?2)
(?R<named>)	Recursively refer to named group.
(?R'named')