The current draft spec has this for pointerType:
Should this be a string rather than enumerated constants? What about extensibility?
We need to resolve this. In particular, for scenarios like bug 20218 (where you could imagine different vendors adding different extensions, and certainly want websites to be able to opt-in to understanding new types of pointers) I think a string is preferable to an enum. Also a string seems more consistent with the DOM event model.
Per 12/11 telecon resolution, making change that pointerType will be a DOMString. Normative values are provided for mouse, pen, and touch input. An enum is not used in order to facilitate synthetic events (e.g. from future polyfills) providing arbitrary values.