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Scripts > Token definitions > Regular expressions > Groupings


Parentheses serve two purposes:


1. To group items together into a sub-expression


If expressions are grouped into a sub-expression, operators like the repetition operator, can be applied to the whole group. For example the expression "(ab)*" would match all of the string "ababab".



2. To mark what generated the match


When the whole expression has matched, both informations can be accessed (via xState):  on what the whole expression matched and on what each sub-expression matched. Sub-expressions are indexed from left to right starting from 1; sub-expression 0 is the whole expression. The according parts of text are obtained by


str s = xState.str(index);


It is permissible for sub-expressions to match null strings. If a sub-expression takes no part in a match - for example if it is part of an alternative that is not taken - then xState.str(index) will return an empty string.







This page belongs to the TextTransformer Documentation

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