type InvalidContext

              object --+                        
                       |                        
exceptions.BaseException --+                    
                           |                    
        exceptions.Exception --+                
                               |                
        exceptions.StandardError --+            
                                   |            
          exceptions.ArithmeticError --+        
                                       |        
                        DecimalException --+    
                                           |    
                            InvalidOperation --+
                                               |
                                              InvalidContext

Invalid context. Unknown rounding, for example.

This occurs and signals invalid-operation if an invalid context was detected during an operation. This can occur if contexts are not checked on creation and either the precision exceeds the capability of the underlying concrete representation or an unknown or unsupported rounding was specified. These aspects of the context need only be checked when the values are required to be used. The result is [0,qNaN].