Common User Agent Problems identifies typical problems with Web browsers without chastising vendors directly for non-compliance.

Starting with the subtitle, "Once Upon A Time, A User Agent...", the document:

"explains some common mistakes in user agents due to incorrect or incomplete implementation of specifications, and suggests remedies. It also suggests some 'good behavior' where specifications themselves do not specify any particular behavior (e.g., in the face of error conditions)."

Rather than challenging W3C members directly,

"This document does not incriminate specific user agents. W3C does not generally track bugs or errors in implementations. That information is generally tracked by the vendors themselves or third parties."

The document is broken down into usability (notably customization and user interface issues), rendering (style sheets and HTML link types), protocol implementation (HTTP processing and MIME content type negotiation), and URI handling.

While a useful reference - even for HTTP and URI processing in non-browser situations - and somewhat XML-aware, the document omits a fair number of issues specific to the integration of HTML and XML.

Notably, no mention whatsoever is made of XHTML or namespace handling. Currently, Mozilla, Opera, and Internet Explorer 5 use different namespace mechanisms to identify HTML content within XML documents, for instance. The document also leaves out DOCTYPE declaration processing, used by some browsers to distinguish different categories of HTML/XHTML content.

Slashdot has a discussion of the document.