How to check whether the PHP code is compatible with the exact PHP version in PhpStorm?

Question 

An old code should be converted to a newer PHP version. How could PhpStorm help with detecting backwards-incompatible updates?

Answer 

To make sure that the code is compatible with the exact PHP version:

1. Open Settings | PHP | and set the PHP Language level to the desired one:
   

2. Click on the root of the project in the Project tool window.

3. In the main menu at the top of the IDE, select Code | Analyze Code | Run Inspection by name:
   

4. Find the Language level inspection:

   

5. Adjust Scope in the next window if required and press OK.