VOTable and VOUnits

[Markus Demleitner]

Hi Mark,

On Thu, May 18, 2023 at 04:59:28PM +0100, Mark Taylor wrote:
> Do people have opinions on which it should be?

Well: Can we get away with a MUST?  By the book, I don't think we're
allowed to do that, because it would make a large proportion of
VOTables that were previously valid invalid in one fell swoop.

On the other hand, I don't think it has any *operational*
consequences in that things that worked before stop working (e.g., a
new client starts refusing old VOTables), and for all I care about
"breaking change" can only be sensibly defined operationally.  To
make that a bit clearer, we could even hedge a bit: "for historical
reasons, clients MUST NOT entirely reject VOTables with non-VOUnit
compliant unit strings; it is recommended to just treat such columns
as unitless and issue a warning".

On the other hand: "issue a warning" is exactly what SHOULD is for.
So, I'd say we ought to have SHOULD in this version and perhaps
something like "it is planned to make this a hard requirement in
later VOTable versions" or so.

          -- Markus