by Jason Snell
The chain, or opening files in macOS
Howard Oakley of Eclectic Light Company has a deep dive on how your Mac knows what app to open when you double click a file:
In the days of Classic Mac OS, that was accomplished using the infamous Desktop Database, which recognised files and apps by means of their Creator and Type, two codes consisting of four characters each. A great deal has changed since, for the better. This process now relies on a chain of information to work out which app to launch to open any file. Although that chain can go wrong, in general it’s far more reliable now and seldom needs any user intervention or maintenance.
As much as I initially missed the old Type/Creator system, and as much as a dislike relying on file extensions (and keep them hidden by default on my Mac!), I do love being able to arbitrarily command that all files of a given type open in my preferred app, all right from Finder’s Get Info window.