Is there a *relatively* complete description of instre1, instre2 and other langs.xml classification tags?

[Bernie Baillargeon]

several posts here and on gitter refer to adding language support via langs.xml, but the tags and keyword groupings seem to have a purpose -only certain things should be instre1 and others instre2, etc., same w/ type1 - type8 and per-language classifiers DELIMETER, COMMENT, FUNC1, etc…
a single source reference of the intent for these groupings would really help out.