HTML level 1 headline tags.
This is a skeleton command (see `skeleton-insert').
Normally the skeleton text is inserted at point, with nothing "inside".
If there is a highlighted region, the skeleton text is wrapped
around the region text.
A prefix argument ARG says to wrap the skeleton around the next ARG words.
A prefix argument of -1 says to wrap around region, even if not highlighted.
A prefix argument of zero says to wrap around zero words---that is, nothing.
This is a way of overriding the use of a highlighted region.