'xs:NMTOKEN with letters': {|xml|| ABCD |}. 'xs:NMTOKEN with numbers': {|xml|| 123_456 |}. 'xs:NMTOKEN with leading spaces that get removed while parsing': {|xml|| starts_with_spaces |}. 'xs:NMTOKEN with trailing spaces that get removed while parsing': {|xml|| ends_with_spaces |}. 'xs:NMTOKEN with spaces in-between'(fail): {|xml|| |}. 'xs:NMTOKEN with empty value'(fail): {|xml|| |}.