ThisVer

XML: The XML version of the spec is the one that Michael and I actually authored, and should be considered authoritative. It contains substantially more information (including a partial revision log, and some amusing comments) than appear in any of the HTML or print versions. It was edited mostly in GNU Emacs.
HTML: The version you are reading, and the one at the W3C site, were generated by a Java program I wrote that uses my XML processor (Lark) to read the specification, and a lot of custom code to generate the corresponding HTML. The HTML version is the best version to use if you are a programmer and want to drill down into the spec and check up on the details of definitions and productions.
PostScript: The PostScript version was created by using Jade, a public-domain DSSSL engine; this was driven by a stylesheet that created an RTF version of the spec. The RTF version was hand-edited in Microsoft Word to fix up pagination and so on, and to generate the PostScript. All this work was done by Jon Bosak.
PDF: The PDF version was created from the PostScript version using the Adobe Distiller product. It is probably the one to get if you want to print out the spec for easy reading. It is interesting to note that the HTML version is slightly larger than the XML version, while the PDF version is slightly smaller.