For my purposes, if the chapter number and the subheading use similar CSS, I will use a <br/><span>...</span>. Otherwise, I will use the chapter number in it's own header and the subheader with it's own CSS and then use a title="" to have both in the ToC. If I don't use a subheader, the title would be used to add Chapter ( i.e. title="Chapter 1">1.< ) since I prefer to not have naked numbers in the ToC.
Code:
<h3 title="Chapter 1">1.</h3>
Code:
<h3 title="1: The End of the Beginning">1.</h3>
<p class="subheader">The End of the Beginning</p>
If necessary, regex is very helpful in generating the title element.