Bug 5921, bug 6284, bug 6718 and bug 6818 relate to XHTML resources that cannot be successfully decoded or parsed to create a DOM tree.

The mobileOK Basic Tests 1.0 specification does not define any generic error message to represent such errors. The only FAIL that more or less matches this case is:
 CONTENT_FORMAT_SUPPORT-4
 [If the document is not an HTML document, FAIL]
... but the message is more intended to be triggered when a DOM tree does not have "html" at its root than in any other case. In particular, it's a bit obscure from a usability perspective.

Some more generic error messages might be worth triggering in MAIN_DOCUMENT, e.g.:
 FAIL: the resource was thought to be text but could not be decoded as such [MAIN_DOCUMENT-1]
 WARN: unknown encoding detected "[specified encoding]" [MAIN_DOCUMENT-2]
 FAIL: the supposedly XHTML resource could not be parsed as such [MAIN_DOCUMENT-3]

We're not supposed to add failures that are not defined in the spec, but then we've already added the MAIN_DOCUMENT test anyway and these errors would help users understand that the major problem has to do with the whole document and not part of it. CONTENT_FORMAT_SUPPORT-4 would still be raised when these errors occur, preserving the rules for mobileOK-ness.

[to be discussed]