my question of some time ago (which got no reply) was along a similar 
line ; by introducing the isA field, the new node inherits the fields 
from (multiple) parents.  Therefore, should these be declared 
(again) in the fields definition within the new node?  I say they 
should not - the whole point is that by declaring the node is based 
on some standard type, any parser/run-time not capable of 
understanding the new type can take some gui>  as how to interpret 
the node otherwise.  For example
blueGlass {
  isA "Material"
  fields [ MFFloat refractiveIndex ]
  
  diffuse 0 0 1
  refractiveIndex 1.1
}
could be rendered opaque if a renderer cannot support refraction - 
the Material fields are implied from the "isA" statement.
As an aside, I have implemented this in my VRML parser
Any comments?
 
> 3) The MFString type, while being a logical extension to the SF/MF 
> convention, needs to be defined explicitly.
The name says it all.  M=multiple, therefore MFString = multiple 
strings, seperated by comma's and enclosed in [ ] as with all other 
MFtypes
Hope that helps
Steve
=========================
Steve Ghee ( [email protected] )
Director of Technology
Division Ltd   
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