Thanks all @cpelley @marqh  @bblay : Well spotted + great work, guys!

I think this could be a really important gotcha.  The area certainly needs looking at --  we are ignoring even the master table version at present.
In particular, this might mean we will need a more powerful lookup/matching strategy than just dictionary keys...
(See also below, on the type of the 'set_height' key)

> Perhaps we can separate the capability (which must be in the Iris core) from the details (

I'm not so bothered by this, it seems to me a separate issue, or at least potentially so ?