The key_name production is what allows a keyword to also be used as an object key in $.keyname syntax. The trim keywords (ltrim, rtrim, btrim) were added there, so $.ltrim as a key works. But $.lower,
$.upper, $.initcap, $.replace, and $.split_part as keys would all break.
Ooh, right. It has been so long since I looked at this stuff that I forgot. Thanks for the reminder.
