The text of S02, S03, and S04 still contain references to the
now-defunct "statement_modifier" grammatical category.
Also, what's the reasoning behind specifically disallowing _all_
statement modifiers to "do" blocks (as opposed to forbidding just
looping statement modifiers)? Is this legacy from when the
distinction wasn't being made, or is there still a valid reason for
forbidding conditional modifiers?
Finally: when used as a statement modifier, is "given" considered to
be conditional or looping? (Gut instinct: conditional.)