The <attr:> token enables you to apply different texture maps based on the name of the attribute that is assigned to the mesh. It is supported in the form <attr:name index:name default:value>. The tag will look for the named user data (as a string). The index and default tokens are optional; if the index is used, the UINT user data is found first, and the main attribute then must be an array of strings it indexes into. Among other techniques, this allows e.g. facesets, where you can list the faceset names once each in a constant array, and then have a uniform UINT assigned to each face specifying which faceset the face is a member of. Finally, the default, if present, is substituted if the user data cannot be found for any reason.