Matt,
It looks like another person had a similar question before, see the following thread:
https://supportforums.cisco.com/discussion/9697836/can-use-axl-or-other-api-get-calls-progress
Also, according to the comments seen on that post, I was able to find the JTAPI developers guide, see more information below:
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/jtapi_dev/8_6_1/jtapidevguide/overview.html
If this still does not satisfy your question then, the best you can do is post this inquiry on the Cisco Developer Network on the following link:
https://developer.cisco.com/site/devnet/home/index.gsp
Hope this information helps,
Marco Rojas.