empty param values in votable

[Carlos Rodrigo]

Hi

the astropy people have found an issue in one SVO service votable and I am not sure if I understand
the VOTable standard about this.

The main point is:

<PARAM name="INPUT:Instrument" datatype="char" arraysize="*">
<VALUES>
<OPTION name="All" value=""/>
<OPTION value="90prime"/>
<OPTION value="AcqCam-N"/>
</VALUES>
</PARAM>

is correct? Is it valid to specify value="" for an OPTION element?

you can see the actual votable at:
http://svo2.cab.inta-csic.es/theory/fps/fpsold.php?FORMAT=metadata

A related question:

Is it valid to write:

<PARAM name="Instrument" datatype="char" arraysize="*" value=""/>

that is, specifying an empty value for a PARAM element?

And, a last question, having a VALUES sub-element replaces the need of having a VALUE attribute for
params?

Thanks for your comments

Carlos