In IDEA 15 you're able to use the below switches to toggle the case of captured expressions. This is now officially documented since this version was released.

    \l: lower the case of the one next character

    \u: up the case of the one next character

    \L: lower the case of the next characters until a \E or the end of the replacement string

    \U: up the case of the next characters until a \E or the end of the replacement string

    \E: mark the end of a case change initiated by \U or \L

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Here is an example usage (as the documentation is not clear):

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    find: (\w+_)+(\w+) replace: \L$1$2\E

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The above will convert FOO_BAR_BAZ to foo_bar_baz etc The $1 refers to the first found capture group (in parenthesis), $2 to the second set, etc.