See Mannequin Tags & Tag Definitions for more information on this concept.
Tag definition files are referenced by the Controller Definition File (xxxControllerDefs.xml), any Animation Database File (ADB), and (optionally) by FragmentID Definition Files. See the overview picture on the page about Mannequin Files.
Tag definition files can include other tag definition files hierarchically.
Creating a Tag Definition File
Tag Definition files can be created in the Mannequin Tag Definition Editor.
Tag Definition files are stored in the Animations/Mannequin/ADB/ folder. This is not an absolute requirement for the engine, but the Mannequin Tag Definition Editor only looks for tag definition files in this folder currently.
The filename typically ends with Tags.xml. Again this is not an absolute requirement, but the editor will filter on this file ending.
Editing a Tag Definition File
Tag Definition files are edited in the Mannequin Tag Definition Editor.
However, you cannot edit the hierarchical inclusion of tag definition files in this editor. To use this advanced feature see the File Format section.
This is an example of the current format (version 2)
The root element TagDefinition should contain the proper version number.
The Imports element contains a list of other included tag definition files. These are merged together during loading. (similar to an #include statement in C code) In this example we refer to a shared itemTags.xml tagdefinition which could contain tags related to item handling, which are shared between multiple character types.
The Tags element contains the list of individual tags (Tag) and tag groups (Group). Each individual tag can get a priority. The default priority is 0.