There are some minor internal inconsistencies in the HTML 3.2 specification.
The specification is relatively short and technical, and consulting the older HTML 2.0 specification (also known as RFC 1866) can be useful, since the current HTML 3.2 specifications can sometimes be understood only be assuming HTML 2.0 as a background document.
In order to understand the HTML specifications exactly, some fluency in reading SGML (the metalanguage used to describe the syntax of HTML formally) is required. SGML as a whole is rather complicated, and the SGML standard is only available in printed form. However, for the purpose of understanding the SGML descriptions of the syntax of HTML (that is, HTML DTDs), the following material usually gives you enough information:
Probably the most comprehensive source of information about SGML is the following book (which contains the SGML standard with annotations as well as tutorial material): Goldfarb, Charles F.: The SGML handbook. Oxford, 1990. Clarendon Press. ISBN 0-19-853737-9. UDK: 681.3.06.