Unicode canonical equivalence vs. compatibility

UnicodeEquivalence.swift

let precomposed = "é"
let decomposed = "e\u{301}"
// `==` for strings means canonically equivalent:
assert(precomposed == decomposed)

let letters = "ffi"
let ligature = "ffi"
// The ligature and its decomposition are *not* canonically equivalent:
assert(letters != ligature)

// But they are *compatible* (used for searching etc.)
import Foundation
assert(letters.decomposedStringWithCompatibilityMapping
  == ligature.decomposedStringWithCompatibilityMapping)