DEELX Extended Syntax: Conditional Expression

Return: Content | Prev: Independent expression | Next: Recursive expression

Conditional Expression

According to a certain condition, conditional expression matches one of two options.

Remarks

The condition can be:

1. Whether a certain group captured or not.
2. Whether a certain expression can match at current position or not.

Conditional expression and description:

Expression	Characteristic	Description
(?(1)yes|no)	Is number	If group 1 captured, match yes, or else match no
(?(?=a)aa|bbb)	Assertion	If next char is 'a', match aa, or else match bbb
(?(xxx)aa|bbb)	Not named group	If there is no named group 'xxx', same as (?=xxx)
(?(name)yes|no)	Is named group	If there is named group 'name', captured or not

More:

1. If it is RIGHTTOLEFT mode,  (?(xxx)aa|bbb) is same as (?(?<=xxx)aa|bbb) .
2. If there is only one option, the option will do match if the condition success.
3. If there are more than 2 options separated by "|", only the first "|" is regarded as conditional expression's separator. For example: (?(?=xxx)yes|no1|no2), if condition success, "yes" matches, or "no1|no2" matches.