SIA and FORMAT=ALL comments

[Tom McGlynn (NASA/GSFC Code 660.1)]

We recently had an issue validating an SIA (V1) service which did not 
accept the syntax

    FORMAT=ALL

While I'd originally thought that support for this is clearly mandated 
by the standard, reality seems a bit more nuanced.  There is no explicit 
statement that FORMAT=ALL be allowed and there is an explicit statement 
that support for any given format is optional. However there is a note 
that if no format is given then it should be treated as FORMAT=ALL and 
the FORMAT parameter is optional.  On balance I'd take this to mean that 
support for FORMAT=ALL is indeed mandatory, but I'd have appreciated a 
clearer statement.

In SIA V2 I see that the SIA V1 special format strings, including ALL 
and GRAPHICS_ALL, seem to no longer be supported.  I presume this was 
intentional but  being able to request all available formats without 
knowing in advance what they are seems like a nice feature.  Are we 
allowed to continue to support these in the new version?  The current 
language seems to suggest not since the value for FORMAT looks like it's 
required to be mime-type.  The text in 2.1.19 seems actually to be 
designed to be for the format result column rather than the input 
keyword, but perhaps I misunderstand.

      Tom

P.S., I'm sure this has been mentioned before but there is something odd 
about 2.1.18 in at least the HTML version of the standard I'm seeing at 
http://www.ivoa.net/documents/SIA/20150730/PR-SIA-2.0-20150730.html#toc11 where 
it appears to be blank.