Where is the XML manifest file located that controls the script lab sidebar?

Question

I am developing a sidebar for MS Word and need to make a few changes in the manifest, but all of the articles that tell me how to make those changes just take it for granted that the reader already knows where that file is located.

My immediate need is to derive content from the Word document.body and display it in a new browser window outside of the sidebar. I would love to hear from you if you know a good way to do that.