Linking macOS-provided software breaks things only in `/usr/local` prefixes, hence the `default_prefix?` check, which was included when our only default prefix on macOS was `/usr/local`. Now that we install into `/opt/homebrew` too, the default prefix check is needlessly restrictive.
Library
This directory contains all the code run by the official brew command in Homebrew and all formulae (package descriptions) in taps (repositories containing formulae) in Taps subdirectories.