Documentation for ethers.getContractAt()

Question

Can somebody please point me to the documentation (official or otherwise ) that explains the function ethers.getContractAt():

the original context of this is as follows:

vrfCoordinator = await ethers.getContractAt('VRFCoordinatorMock', VRFCoordinatorMock.address, signer)

and the full code can be found here... https://github.com/PatrickAlphaC/all-on-chain-generated-nft/blob/main/deploy/02_Deploy_RandomSVG.js

In the absence of such documentation, an explanation would be much appreciated. Thank you!