Liza Daly from threepress.org has just released an article outlining problems she is having with users uploading invalid ePub formatted documents to Bookworm; an online ePub book reader. It’s very important for anyone developing ePub eBooks to produce valid markup. Not only will Bookworm give desirable results when rendering, but you’ll also be covering yourself for any future rendering engines and conversions you might need to do.
It’s actually quite surprising how many errors are showing up from files submitted to Bookworm. You should go over to the threepress blog for a full explanation, but here’s a list of the main errors;
- Missing required attributes in the metadata
- Metadata that hasn’t been proofread
- Improper nesting of the ePub zip file
- Items declared in the OPF file that are missing from the archive
- Invalid XHTML
Points 1 to 4 are really quite vital, although it is understanable for many documents to have invalid XHTML. Still, if it is within your means, I would try to control this the best you can.
I have plans to write some detailed articles regarding the creation of both the NCX and OPF files found in an ePub document, so keep a lookout for those.