I can't think of one. But you don't have to create a full custom property, you can use PropertyControlClassFactory.Instance.RegisterClass to replace the control used to edit strings with the a derived class. However, in that scenario, you'll need to find a way to only limit the properties you want to be limited (and not all string properties). If you are lucky enough to be using EPiServer 6 you should be able to do this using property settings. Since you can't set the property settings for built-in properties you have to leave the default behaviour as-is, but you can add the possibility to, for instance, specify a regex for the input to be tested against.