Token Highlighting cannot be used with multiple files.
If two files already open when tracking begins and highlighting is on, it will not display and switching to another file crashes the application.
However, if one file is open at the start, it seems possible to close the current file and open another. Opening two file will throw and error that may or may not crash the application (a dialogue may appear only indicating the error or you will be crashed back to the instance of visual studio that launched the plugin testing environment).