Editing Comments on HN, what are the norms?

Generally, if you edit a post/comment mark it as edited with a note as to context. e.g. * edit - fixed spelling. etc. This seems to be the norm I see and I have followed here.

Personally, I'll edit a comment if no one has already commented or voted on my post, if someone has commented or voted then I'll add a reply to my own comment with clarification instead of editing, and only if it is truly necessary for clarification.