Difference between hatch and hatchling?

[iskarian]

This might sound like a stupid question, but I figured if I had it even after reading the basic docs, someone else will, so...

What is the difference between hatch and hatchling? Hatchling is the "build backend," yes, but what does that mean? Do I need to separately install hatchling? The install instructions for hatch make no mention of doing so, but then why are there distribution-specific hatchling packages?

(Should this be clarified somewhere in the docs?)

[ofek]

Added a note! https://hatch.pypa.io/dev/install/#build-system-availability