I am thinking of writing an introduction to interacting with wheelchair users

Like: guidelines on when it's appropriate to touch a chair; guidelines on asking if help's wanted; guidelines on talking to someone using a chair (and therefore not at standing height) -- with the understanding that people vary. (Largely because I have come up with a rule-of-thumb about touching chairs that I am failing to phrase as a standalone post, so.)

Interested? Got things you'd like addressed?