The use statement tells Keyman to switch processing to a new group; after Keyman has gone through the new group, and any other nested groups, it will return to the previous one. The use statement can be used with the match and nomatch rules; it will work the same way.
The current output is moved to the context before the new group is entered, so the new group will see the output from the fired rule as its context.
any(Vowel) + any(DiacriticKey) > context use(AdjustVowels)
The use statement was introduced in Keyman 3.0.