Codeigniter php framework URLs look like the above.
I'm surprised that apache maps this request to index.php at the server root. I expected it to interpret /index.php/abc/def as a file 'abc' in a directory /index.php/abc, and as a result a 404 Not Found (given that no such file exists).
Can anyone explain why index.php gets executed instead? Is there a document that explains apaches 'map request to resource' strategy, that would explain the above observation?
Because when it looks in the root folder it sees index.php is a file not a folder, so it executes that file rather than looking inside it (if it was a directory) for the next element of the path.
The rest of the "path" then becomes an unconventional querystring of sorts
index.php is an actual file in the document root of your project. The framework is setup to route all requests to this file. It is also typically called a "bootstrap" file. The bootstrap file is responsible for starting up your application and ultimately getting your request where it needs to go.
There is a router in the framework that takes in the uri, everything after index.php and then maps that to a controller/action combination.