XDT Transformation Tool
XDT Transformation tool is a command tool based on
XDT (web.config) transform engine, which allows you to run XDT transformation on any XML files.
Scott Guthrie:
"In most real-world deployment scenarios, the web.config file you use for development is different than the one you use for production deployment. Typically you want to change environment settings like database connection-strings, making sure debug is turned off, and enabling custom errors so that end-users (and hackers) don’t see the internals of your application."If you want to know more about XDT Transformation Syntax, follow this link
Deployment Web Application Project. To know how to start using XDT Transformation Tool follow this link
Documentation.
Blog posts:
Also you can find posts on Russian
Config Transformation Tool