code: @Override
    protected Object doExec(Element element, Object scope, String booleanExpression, Object... arguments)
    {
      // returned value is interpreted as branch enabled
      // boolean expression argument is true if branch should be excluded, so we need to inverse it
      return !Boolean.valueOf(booleanExpression);
    }
docs: Execute EXCLUDE operator. Returns branch enabled flag, that is, true to indicate branch is to be included in resulting
  document. Since exclude operator has opposite logic we need to negate given boolean expression; so, if operand is 'true'
  meaning the branch should be excluded this method returns false.
  
  @param element context element, unused,
  @param scope scope object, unused,
  @param booleanExpression boolean expression, 'true' or 'false',
  @param arguments optional arguments, not used.
  @return branch enabled flag.