docs: @Check
  	public void checkContainerType(SarlAgent agent) {
  		final XtendTypeDeclaration declaringType = agent.getDeclaringType();
  		if (declaringType != null) {
  			final String name = canonicalName(declaringType);
  			assert name != null;
  			error(MessageFormat.format(Messages.SARLValidator_28, name),
  					agent,
  					null,
  					INVALID_NESTED_DEFINITION);
  		}
  	}