We have a few server configuration options like e.g. wsrep_slave_UK_checks and wsrep_slave_FK_checks that unfortunately use a mix of lower and upper case letters.
As the vast majority of option names only uses lower case letters it often happens that one e.g. types wsrep_slave_fk_checks all lower case, and ends up with startup failures due to "Unknown option" errors.
As it is probably too late to rename the options by now, and as I am not aware of any two option names that only differ in letter case, I'd suggest to make option name lookups and comparisons case insensitive. As SQL level "SET variable=..." is case insensitive already anyway that would actually improve consistency in option name handling
Alternatively: identify all existing mix cased options, and create all-lower-case aliases for them?