10.1 disallowed use of non-parenthesized UNION parts that have ORDER or LIMIT clauses, according to the SQL Standard. That was a merge from MySQL-5.6.
returns an error starting from 10.1:
However, if I use LIMIT in combination with ROWS EXAMINED:
it returns a result instead of an error:
It should be fixed to require parentheses as well, like in case of a "normal" LIMIT clause.
Most likely, LIMIT ROWS EXAMINED was just forgotten during the merge.
The documentation at:
Individual selects can contain their own ORDER BY and LIMIT clauses. In that case, the individual queries need to be wrapped between parenthesis.