title_body: How to split an EPUB into multiple files of one chapter?
upvoted_answer: If each chapter is formatted as an h1-h6 tag or marked with a unique style, you could use Sigil to insert split markers. For example, if all your chapter headings are formatted as &lt;h1&gt; tags, you'd use:
  
  Find:&lt;h1
  
  Replace:&lt;hr class="sigil_split_marker" /&gt;&lt;h1
  
  Then select Edit > Split at markers.