I have used a couple web/page different authoring tools now. Some assign a default .HTM, and some assign a default .HTML to HTML docs. Then I start noticing on the web what's out there, and there's a mixture. Seems like there ought to be a standard for this?

I can see a point in using .HTM, it fits a 3-char extension suffix which might be a good idea for interaction with various software. Any comments as to which is preferred, or is there some subtle difference I'm not aware of?