| ERROR | circular reference detected in schema component named ~S |
| CAUSE | An attempt was made to use a circular reference. This is not allowed. For example, it is not possible to return to an element declaration by repeatedly following the {substitution group affiliation} property. Or, within the {particles} of a group there must not be at any depth a particle whose {term} is the group itself. |
| ACTION | Modify one of the schema components in the loop. |