Let's take the following OASIS catalog TestXMLCatalog.xml :
Add it to netbeans catalog with Tools> DTD and XML schemas then "add Catalog"
and selecting "Oasis catalog resolver" an browsing to the file above (TestXMLCatalog.xml).
As a result a new node appears as "Resolver at TestXMLCatalog.xml" but it has no child.
Add the following line to TestXMLCatalog.xml
<public publicId="Schema public Id"
add anew the modified catalog, in the catalog view the node "Resolver at TestXMLCatalog.xml" has only one child : the one corresponding to the public entry.
Sounds like a bug - not sure if this ever worked. I don't think this is considered a primary IDE feature, lowering priority to P3.
Just to confirm - what is the main reason for adding the catalog to the registry? To provide code completion based on the schema? That should normally work even without adding a catalog.
A catalog is very handy when you work with no internet access.
You can manage to avoid validating processes (e.g. in a build step of a build suite) to fail when facing network failures.
Please note that Netbeans off the self catalogs are not comprehensive.