code: public void execute( EnforcerRuleHelper helper )
          throws EnforcerRuleException
      {
          Log log = helper.getLog();
  
          try
          {
              log.debug( "Echo condition : " + this.condition );
              // Evaluate condition within Plexus Container
              String script = (String) helper.evaluate( this.condition );
              log.debug( "Echo script : " + script );
              if ( !evaluateCondition( script, log ) )
              {
                  String message = getMessage();
                  if ( StringUtils.isEmpty( message ) )
                  {
                      message = "The expression \"" + condition + "\" is not true.";
                  }
                  throw new EnforcerRuleException( message );
              }
          }
          catch ( ExpressionEvaluationException e )
          {
              throw new EnforcerRuleException( "Unable to evaluate an expression '" + condition + "'", e );
          }
      }
docs: /*
  (non-Javadoc)
  
  @see org.apache.maven.enforcer.rule.api.EnforcerRule#execute(org.apache.maven.enforcer.rule.api.EnforcerRuleHelper)