Editing WoW:XML attributes (section)

=== inherits ===
(string) - the name of template to use as a base type for this element. Inherited elements, called templates, are normally marked with 'virtual="true"'. Some element types can inherit other types, such as FontString inheriting from Font. Generally matching properties of the inherited type are used as though they are properties of the inheriting element. The names are not case sensitive, such that inherits="BobBB" will still inherit from an element named name="BobBb" virtual="true".

The 'inherits' attribute supports multiple-inheritance, where more than one element can be used as a base. Names are separated by with commas, and names farther to the right take precedence over the preceding ones, like '<Button inherits="OneTemplate,TwoTemplate">'. Properties will be used first from "OneTemplate" and then 'TwoTemplate', but if 'TwoTemplate' has a matching property with 'OneTemplate', then 'TwoTemplate' will override 'OneTemplate'. Some types have special rules for exactly how properties and child elements get inherited.