Catch "Subtitle" styles
See #71 (closed) for Boyles files
The chapter's subtitle ("A Startling Turn of Events") doesn't get promoted to a heading. There are 2 issues here:
- It is labeled as a Word style "Subtitle." This should be one of the styles that XSweet pays attention to for consideration as a header. In this entire book, the author's used styles h1-4 to mark the different heading levels correctly. I think the conversion pipeline is noting this, as all the properly labeled headers are coming through accurately, so it would be good to stir class="Subtitle" into the mix too.
- (more of a note to self) Even if the author hadn't styled this, it's short and centered, so should be caught by the "if it's centered and short it's a header" rule, once that is implemented.