(a)
<H4 style="display: run-in;">A Heading.</H4>
<P>This is a paragraph of text which has a run-in heading at
its beginning.  It doesn't look like an H4, does it? </P>

(b)
A Heading. This is a paragraph of text which has a run-in heading at
its beginning.  It doesn't look like an H4, does it?