Only to amend what has been said. Working strickly from pentatonics, whether major or minor, the system will work
extremely well. Pentatonics are only slightly extended arpeggios. Most pentatonic players learn to modify these scales through trial and error and/or help. This system will work even with all of this. It's like superimposing or using an overlay above a chord... or change (same meaning).
Many tunes do not stay in one key. They're called tonal centers. The system I espouse will get one through tonal centers, even with pentatonics, if the scales are learned thoroughly... only 5.
This system is a system for guitar players, that boils jazz, rock, pop and country into a few short pages. And it always works. This system will appear in many different ways depending upon curricula, but this is it in a nutshell.