What is the difference between a module and extension?

can someone explain:

  1. what are the necessary criteria for Yii to find a module? What needs to be setup and what general steps does the framework take to load a module versus some other component like a widget or an extension.

  2. what is the difference between a module and extension, when should you use module instead of extension and vice versa?

  3. What would prevent Yii from locating and loading a specific module if all other parts of a webapp were functional?

These questions are for better general understanding of the framework, and how to troubleshoot this class of problem not for specific problem noted above. If you are interested in details of the specific problem or think you may have same issue my steps to resolve the problem and config info can be found here:




Thank you kindly!

P.S. I did RTFM but just not getting it ???