[imp] Add some documentation

### Description
The code lacks in-code documentation and it's necessary to be added. It will not only improve the development process of the other contributors but also can be used later for the documentation generation process. Proper guidelines should be defined on where and how to put the in-code documentation and the format which needs to be followed.

### Expectation
The code is properly documented with in-code documentation.

No files, tests, or entry points are named. Start by surveying the C++ codebase and its existing comments to determine the documentation scope and conventions; done means the agreed guidelines are defined and the relevant code has consistent in-code documentation suitable for later generation.

Written by the indexing model from the issue text.