4. How do you use a catalog?

Resolvers have been around from the beginning, so most APIs have some support for them. For example,
```
XmlReaderSettings settings = new XmlReaderSettings();
settings.XmlResolver = MyXmlResolver;
```
Many applications support them from the command line; Saxon has -catalog, for example.
- (To use XML Resolver with Saxon 10 or earlier, you actually have to pass a few other options as well.)