Major Some system query options ($filter, $orderby) allow whitespace around the equal sign ($filter=Name eq 'Ralf' / $filter = Name eq 'Ralf'), others ($expand, $format, $inlinecount, $select, $skip, $skiptoken, $top) don't allow any whitespace around the equal sign or the clause-separating comma, and one ($select) only allows it after the equal sign.
Similar situation with whitespace before or after a clause-separating comma: $select allows it before and after, $orderby allows it after the comma but not before if preceded by "asc" or "desc", $expand does not allow whitespace at all.