nsIResProtocolHandler Interface

 Gets the substitution for the root key.

 @throws NS_ERROR_NOT_AVAILABLE if none exists.

nsIURI getSubstitution(in ACString root)

 Returns TRUE if the substitution exists and FALSE otherwise.

boolean hasSubstitution(in ACString root)

 Utility function to resolve a resource URI.  A resolved URI is not 
 guaranteed to reference a resource that exists (ie. opening a channel to
 the resolved URI may fail).

 @throws NS_ERROR_NOT_AVAILABLE if resURI.host() is an unknown root key.

AUTF8String resolveURI(in nsIURI resURI)

 Sets the substitution for the root key:
   resource://root/path ==> baseURI.resolve(path)

 A null baseURI removes the specified substitution.

 A root key should always be lowercase; however, this may not be
 enforced.

void setSubstitution(in ACString root, in nsIURI baseURI)