Which is appropriate .htm or .html?

[jay]

Thanks to all who responded w/r/t my question on SHTML...

I've got another one: what are the rules governing the use of the
.htm/.html extensions in webpages? I've got an .html extension for the
main/index page on our website. The rest use .htm. This doesn't seem to
cause any problems or consternation with anyone. Does it really matter?

Regards,

JHF