Subexpressions

IdealDoc offers support for subexpressions, which allows you to invoke multiple helpers within a single directive, and pass in the results of inner helper invocations as arguments to outer helpers. Subexpressions are delimited by parentheses.

In this case, inner-helper will get invoked with the string argument 'abc', and whatever the inner-helper function returns will get passed in as the first argument to outer-helper (and 'def' will get passed in as the second argument to outer-helper).