Currently the grammar allows ODIN keys to be any primitve value, which would include non-sorting types like Booleans and also intervals, which don't make sense as keys. They should be limited to Strings, Integers, Dates, Times and Date_times.
No impact expected, since all ODIN texts use only String keys anyway.
Changes made to grammar:
* diff of odin.g4: https://github.com/openEHR/adl-antlr/commit/c4a6d48709726fbf7d4c6001c3dfdd73949742e0#diff-5449d4036c9efec5131a26c60747cba1
* current version: https://github.com/openEHR/adl-antlr/blob/master/src/main/antlr/odin.g4#L32
* in published spec: http://www.openehr.org/releases/BASE/latest/docs/odin/odin.html#_syntax_specification (search for key_id)