The Book “Computer Networks: A Systems Approach” is now open source

The epubcheck utility reports more errors than I know what to do with. For example:

Error while parsing file 'value of attribute "lang" is invalid; must be an RFC 3066 language identifier'.

Error while parsing file 'value of attribute "id" is invalid; must be an XML name without colons'.

Error while parsing file 'element "figure" not allowed anywhere; expected the element end-tag, text or element "a", ..., "ul" or "var" (with xmlns:ns="http://www.w3.org/2000/svg")'.

Is this likely a problem in the sources, GitBook, or something else about how the submitter built it?

http://pages.cs.wisc.edu/~pb/cs640.html

We used an earlier edition of the textbook in 2003 (if memory serves, might be +/- a year), and per the link above, looks like they used it as recently as Fall 2017. I remember greatly enjoying the book and the course.