Calibre conversion is not using my command

[Jaws]

I don't entire agree with this solution, primarily because "additive css" (the "h2 + p" on the first line) just doesn't work when there are possibly tables, or possibly graphics (whether glyphs or full-on graphics), or an epigraph, at the beginning of the file. It works for plain text, but a fair proportion of books that one thinks of as "plain text" begin chapters (or sections, if the h2 is used for section headings within chapters) that have elements like this.

I prefer instead to designate a new style in the stylesheet:

.noindent {
  [the rest of the default paragraph code]
  margin-top: 1em;
  text-indent: 0;
  }

and set that search-and-replace up either in normal mode:

</h2>
<p class="calibre1">
[replace with]
</h2>
<p class="noindent">

or, as necessary, just search for the </h2> and manually change the next <p> class to "noindent" if there are elements between the heading and the first actual paragraph of text. It's rare enough to have a book with an excessive number of true chapters that this works for me… and books with 100+ chapters always have other problems that need manual attention! (And even a 100-chapter book can be done in under 3 minutes manually.)

My real point is that there's more than one way to do this, and sometimes a simple search-and-replace-with-nothing is less preferable.