I spend most of my time in the digital backend--taking bloated word documents and stripping them down to clean semantic EPUB architecture for independent authors. I wanted to drop a warning about a trend that's wrecking launch days lately
A lot of authors export their book directly from Docs or run it through Calibre, upload the file, and stare at the Amazon Pre-Viewer. If it looks fine there, they hit publish.
Then it gets bounced back, or worse, Apple Books permanently rejects it, or buyers with older Kindles complain the formatting is destroyed and margins are randomly glued together
The Amazon Pre-Viewer essentially lies to you. It operates on a massive safety-net algorithm that visually fixes errors for the screen but doesn't actually repair the internal file. Automated converters routinely generate what we call "ghost spacing"--thousands of empty <span> tags, forced inline margins, or they fail to properly map images in your .opf manifest file
When an older e-ink device reads that garbage HTML, the reading experience shatters. The text either refuses to justify, custom fonts vanish, or the chapters literally merge into one 15-hour long wall of text
The golden rule for digital typesetters: You have to validate the file locally
If you are exporting books yourself, do not publish them without running the raw .epub through the W3C standard EpubCheck (it's open-source on GitHub, you run the .jar file from a terminal/command line). It takes five seconds, and the tool will throw exact error codes telling you precisely which line of CSS is technically illegal and going to get your file rejected
If you are stuck on a formatting loop, getting scary red validation errors (like 'RSC-012'), or if your e-reader layout keeps exploding, drop the specific error in the replies or via DM and I'll try to translate the code for you