nsIXPointerSchemeProcessors will be called by the XPointer Processor that
 implements the XPointer Framework. This is done for each scheme the
 XPointer Processor finds, in left-to-right order.
interface nsIXPointerSchemeProcessor : nsISupports



 @param aDocument The document in which to resolve the XPointer.
 @param aContext  The XPointer context in which to process aData.
 @param aData     The data in the scheme that needs to be resolved.
 @return          The result of the evaluation.
nsIXPointerResult evaluate(in nsIDOMDocument aDocument, in nsIXPointerSchemeContext aContext, in DOMString aData)