on most other params that accept a semi-colon delimited list we see
list of tags questions must have, semicolon delimited A single primary key identifier or a vectorized, semicolon-delimited list of identifiers.
on /search we see
List of tags delimited by semi-colons that must not be on a question List of tags delimited by semi-colons of which at least one must be on a question
It would help machine readers if the search params were described with the terms semicolon and delimited adjacent anywhere in the description.
List of tags that must not be on a question, semicolon delimited List of tags of which at least one must be on a question, semicolon delimited
UPDATE
found another one on /questions/questions and /questions/unanswered
tagged (optional)
List of tags questions must have
string