Slightly confusing because ambiguous, file parser.c of libxml2 2.9.2 has these
messages. One of them, I'll assume, is shown by WebKit on hitting an attribute
name without a value (i.e. "foo", not "foo='...'") :

   8490:	       "Specification mandate value for attribute %s\n", name);
   9223:                          "Specification mandate value for attribute %s\n",

I take it that these statements either remind the reader
that there is one specification, which mandates,
or that there are two or more specifications,
which mandate. And that this is not to say "mandate value",
possibly as part of a noun triple "specification mandate value",
sounding like the value of a political specification mandate.
(Just illustrating the confusion in a end user's use case.)

If at all correct, then two ways of removing this little ambiguity
would be to substitute "Specifications mandate",
or "Specification mandates". (And adjust the expected
strings in error testing.) Or replace the verb-or-noun
"mandate" with "require(s)", if that's still adequate.

Sorry for the nitpicking, it just took some time to sort
this out when trying to viewing some xhtml document that
had an attribute without a value, which produced a red error
box containing the message.