There is something a bit odd with PL/SQL (or SQL - I'm not sure whether PL/SQL is actually supported. It seems to be sadly unpopular with syntax highlighting plugins.)
A quoted SQL statement seems to defeat the quoting, but only when an earlier line ends with a semicolon.
select blah into blahblah from blahblahblah; -- Semicolon here seems to do it
xxx := 'select select';
Quoting is now reversed.
Looking at other SQL-related issues, I see Syntax highlighting isn't always present in the entire code block also has an example where quoting is broken by a quote that includes a SQL keyword.
Screenshot for posterity:
The actual post where this came up is here: https://stackoverflow.com/a/64183788/230471
Edit: Marking as Lua seems to work better with quoting:
select blah into blahblah from blahblahblah; -- This is a comment
xxx := 'select select';
Quoting is not reversed.