| ERROR | substitution for element ~S is disallowed |
| CAUSE | An attempt was made to substitute an element that violated a constraint. |
| ACTION | Change to a valid new element that can be substituted for the headElement. |
| ERROR | substitution for element ~S is disallowed |
| CAUSE | An attempt was made to substitute an element that violated a constraint. |
| ACTION | Change to a valid new element that can be substituted for the headElement. |