With RPE 1.3 you might notice a new read-only property for all template elements, the ID. This property actually existed since RPE 1.0 but until now it was hidden as it served no immediate purpose.
The serviceability changes, especially the Document Studio Debugger, rely heavily on IDs and so the property has been made visible but remains read-only. You can see the ID in the properties page as well as in the tooltip of each element.
The IDs can be used for search and are also printed in several error messages to help identify the error location:
When loading older templates you might notice warnings in the console about ID conflicts. RPE 1.3 automatically corrects the IDs, ensuring that each ID is used only once per template.