private void LiteralExpressionForm_Load(object sender, EventArgs e)
        {
            source.AddRange(new string[]
            {
                "true", "false", "null"
            });

            // Add all known enum constants
            IEnumerable <EA.Element> enums = EAUtil.findAllEEnums(repository.GetOriginalRepository());

            foreach (EA.Element ruleElement in enums)
            {
                foreach (EA.Attribute attribute in ruleElement.Attributes)
                {
                    if (isEnumConstant(attribute))
                    {
                        source.AddRange(new string[] { ruleElement.Name + "." + attribute.Name });
                    }
                }
            }
        }