[whatwg] <time>

[Kristof Zelechovski]

The most the specification can say about dates without a machine-readable
value attribute is that the user agent should do its best to figure out what
the content means given the language the document is in, perhaps with
precedence given to Gregorian calendar in case of doubt.  The exact rules
for that require too much artificial intelligence to be universally
specified.
Note that the specification does not (and cannot) say that a HTML document
MUST be valid.  It merely describes how the user agent should handle HTML
documents, including ones containing random text.
IMHO,
Chris