missing info in documentation for hook_uc_price_handler

http://api.ubercart.org/api/function/hook_uc_price_handler/2

This doesn't explain the function parameters for the callbacks.
It doesn't explain what the things in the 'options' key are -- the example is quite mysterious.

And it doesn't explain what comes into callbacks.
In particular, the possible values of $context['location'] that get passed to the callback as a product moves through the shopping workflow: node display, cart, checkout, etc etc.

Without this information I can't fix uc_discounts! #578196: uc_discount_price_handler_alter never has any effect.