the symbol ~ is proposed in the draft spec to mean "approximate". For example, 2010-12-15~ would mean "approximately December 15, 2010".
The question was raised "what does approximately mean?" Discussion led to the possible concept of "qualified-" vs. "unqualified approximate".
The definition of 'unqualified approximate' would be:
"An estimate whose value is asserted to be possibly correct, and if not, close to correct."
For 'qualified approximate', some estimate of precision would be appended to the estimate. For example designate a character, let's say &, so that when ~ is encountered, if it is immediately followed by &, that signals that a precision indicator follows, terminated by another &. If a ~ is not followed immediately by & then it is an unqualified approximate. So:
and '123xyz' is the precision indicator.
Rather than a precision indicator, it might be a probability indicator, for example, in the case of 'questionable' as opposed to 'approximate' however I do not want to get into that distinction in this thread.
I do not suggest here what '123xyz' means, or how we go about defining these qualifiers. At this stage I'm simply suggesting this as a syntax to represent (or not) a qualifier.
I would appreciate comments on this approach.