This class should be renamed. These are not generic states but non-concrete states including gap, unknown and missing.

This concept is tied to the verbally ambiguous 'gap' concept and to the use of a gap character (often the en dash '-') in text representations of sequence alignments. In general, this represents the absence of any positively diagnosed Character-State. As such, the gap may be interpreted as an additional Character-State, as the absence of the Character, or as an unknown value. In some cases it is helpful to separate these.