Syntax Tolerance
MQL, which has JSON syntax, is not so hard to write, but sometimes
you can make minor syntax mistakes that renders your query invalid.
The query editor automatically tries to clean up such syntax
errors behind the scene before running the query, so that
you can still make mistakes, such as forgetting quotation marks
and commas (illustrated in screenshot below),
and your query still runs most of the time.
You can also
tell the query editor to explicitly clean up your query by
clicking the Clean Up button. It will quote unquoted strings
and property names, insert missing commas, and remove trailing commas.
(Tip: the keyboard shortcut Shift-Ctrl-Enter will clean up your query
explicitly and then run it.)