Question about HTML-to-EPUB code

ElMiko · 03-25-2025, 10:12 AM

This isn't a conversion problem, per se; it's more of a confusion.

When an HTML file is converted to EPUB and chapter breaks are inserted before <h1> or <h2> tags ([Structure detection] options), at the end of each html "page" in the EPUB I'll see the following code:

Code:

<div class="calibre2" id="calibre_pb_0"></div>

, where "pb_0" increases by two on every subsequent html "page".

This code is not in the original HTML file, the "id" is not referenced anywhere else in the EPUB file (as far as I can tell), and the css for "calibre2" is just "display: block".

Can someone explain what this HTML code is doing, and what—if any—function it has for readability/epub validation/etc. after the converted file has been generated?

kovidgoyal · 03-25-2025, 10:38 AM

That <div> will have been present in the HTML, calibre's HTML splitting code adds ids to all elements that have a page break applied for internal processing.

03-25-2025, 10:12 AM	#1
ElMiko Fanatic Posts: 507 Karma: 65460 Join Date: Jun 2011 Device: Kindle	Question about HTML-to-EPUB code This isn't a conversion problem, per se; it's more of a confusion. When an HTML file is converted to EPUB and chapter breaks are inserted before <h1> or <h2> tags ([Structure detection] options), at the end of each html "page" in the EPUB I'll see the following code: Code: <div class="calibre2" id="calibre_pb_0"></div> , where "pb_0" increases by two on every subsequent html "page". This code is not in the original HTML file, the "id" is not referenced anywhere else in the EPUB file (as far as I can tell), and the css for "calibre2" is just "display: block". Can someone explain what this HTML code is doing, and what—if any—function it has for readability/epub validation/etc. after the converted file has been generated?

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03-25-2025, 10:38 AM	#2
kovidgoyal creator of calibre Posts: 45,611 Karma: 28549044 Join Date: Oct 2006 Location: Mumbai, India Device: Various	That <div> will have been present in the HTML, calibre's HTML splitting code adds ids to all elements that have a page break applied for internal processing.

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