Newbie question about LSP settings -- on_attach

[proofer]

I'd be shocked if this were a real issue; it's posted as a newbie question.

In init.lua there is:

-- LSP settings.
--  This function gets run when an LSP connects to a particular buffer.
local on_attach = function(_, bufnr)
[body of function omitted]

What is it that associates this event handler with LSP? Thanks for any enlightenment...
EDIT (after 3 minutes): Never mind! Thanks for not sending out a posse.