What is the extras Pipfile?

[stokito]

I'm new to Python and trying to run a project.

I have a dependency in the Pipfile:

 somelib = { version = "1.0.0", extras = ["another-lib"] }

As far I understood this should install the somelib and the another-lib with a same version.
Is my assumption correct?
I didn't found anything in the https://pipenv.pypa.io/en/stable/ and anywhere else. It would be really great if anyone can document this.

[matteius]

@stokito some packages define extra dependencies named by specific groups, and that is the purpose of the extras list in the package dictionary.