Parse a designator list.
(parse-designator-list parstate) → (mv erp designors span new-parstate)
This is a non-empty sequence of designators, according to the grammar. We parse the first one, which must exist, and then we check if the next token could start another one, in which case we recursively call this function and then we combine its results with the first designator.
A designator list in the grammar only appears in a designation, where it is followed by an equal sign. So there is no overlap between the equal sign and the possible starts of a designator.