Billing client for studying documentation

I have a php project I have been working on for several months. The client's requirements have expanded to include interfacing to an online service using xml, which I was familiar with but have never worked with prior to this project. I have spent a good number of hours reading up on xml, and learning how to use it to integrate with this online service. I have also spent hours poring over hundreds of pages of documentation for the online service itself. My question is this - should I be billing the client for this time? It is needed to properly work with this framework, but it is not programming time in itself. Googling the topic has been useless. Any advice? Mike