The top-level index.html and RELEASE-NOTES.html files, as well as the HTML files in the Derby demos, need to include a lang attribute in the <html> tag to meet WCAG guideline 4.3:
The image in index.html also needs an alt attribute, to meet WCAG guideline 1.1:
<img src="docs/html/images/logowithtext.jpg" alt="Apache Derby logo" border="0"/>
The frameset in demo/programs/readme.html also needs some fixes to meet WCAG guidelines 6.5 and 12.1. I'll attach a fixed version.
In addition to index.html, RELEASE-NOTES.html, and demo/readme.html, the lang attribute is needed in the following: