DOUBLE_DAGGER

The double-dagger (‡) is used within a Group to delimit the left part, which repeats, from the right part, which separates occurrences of the left part.

The actual method argument (or portion of a method argument associated with this subexpression) must be able to accept some number of occurrences of tuples whose size is the total number of value-yielding subexpressions in the group, plus one final tuple that only has values yielded from subexpressions left of the double-dagger. In the special, most common case of the left side having exactly one yielding expression, and the right side yielding nothing, the inner one-element tuples are elided.