Hi John,
OK, so my adding xlink:type="simple" does not break anything.  Good.
But
      3.2 Markup Conformance
An XML element conforms to XLink if:
  1.
      it has a |type| attribute from the XLink namespace whose value
      is one of "simple", "extended", "locator", "arc", "resource",
      "title", or "none", and
  2.
      it adheres to the conformance constraints imposed by the chosen
      XLink element type, as prescribed in this specification.
So I am asking, politely I hope, to make xlink:type required, so that we 
conform to the xlink spec.
For starters, could all the thredds files that you generate have that 
attribute?
Benno
John Caron wrote:
 we do already allow the "show" and "type" attribute on an Xlink, see:
http://www.unidata.ucar.edu/projects/THREDDS/tech/catalog/InvCatalogSpec.html#XLink 
      XLink Attribute Group
 <xsd:attributeGroup name="XLink">
   <xsd:attribute ref="xlink:href" />
   <xsd:attribute ref="xlink:title" />
   <xsd:attribute ref="xlink:show"/>
   <xsd:attribute ref="xlink:type" />
 </xsd:attributeGroup>
These are attributes from the XLink specification 
<http://www.w3.org/TR/xlink/> that are used to point to another web 
resource. The /xlink:href/ attribute is used for the URL of the 
resource itself. The /xlink:title/ attribute is what should be 
displayed to the user. These are the only two attributes currently 
used in the THREDDS software.You can also add the /xlink:type /or/ 
xlink:show /attributes/. /
--
Dr. M. Benno Blumenthal          benno@xxxxxxxxxxxxxxxx
International Research Institute for climate prediction
The Earth Institute at Columbia University
Lamont Campus, Palisades NY 10964-8000   (845) 680-4450