Explaining decision.

src/implementation.cpp

@@ -89,7 +89,14 @@ public:
     return UNSUPPORTED_ARCHITECTURE;
   }
   WARN_UNUSED bool validate_utf8(const char *, size_t) const noexcept final override {
-    return false; // just refuse the validate
+    return false; // Just refuse to validate. Given that we have a fallback implementation
+    // it seems unlikely that unsupported_implementation will ever be used. If it is used,
+    // then it will flag all strings as invalid. The alternative is to return an error_code
+    // from which the user has to figure out whether the string is valid UTF-8... which seems
+    // like a lot of work just to handle the very unlikely case that we have an unsupported
+    // implementation. And, when it does happen (that we have an unsupported implementation),
+    // what are the chances that the programmer has a fallback? Given that *we* provide the
+    // fallback, it implies that the programmer would need a fallback for our fallback.
   }
   unsupported_implementation() : implementation("unsupported", "Unsupported CPU (no detected SIMD instructions)", 0) {}
 };