| Attribute | Type | Description | Required | 
        
          | assembly | file | The assembly which contains the XSLT extension object. | True | 
        
          | typename | string | The full type name of the XSLT extension object. | True | 
        
          | if | bool | Indicates if the extension object should be added to the XSLT argument list. If true then the extension object will be added; otherwise, skipped. The default is true. | False | 
        
          | namespaceuri | string | The namespace URI to associate with the extension object. | False | 
        
          | unless | bool | Indicates if the extension object should not be added to the XSLT argument list. If false then the extension object will be added; otherwise, skipped. The default is false. | False |