Normative Conventions: pretend Strings aren't iterable

normative-conventions.md

@@ -37,3 +37,11 @@ For the purposes of this guideline `-0` is considered to be an integral number (
 Some APIs intentionally round non-integral inputs, for example as an attempt to provide a best-effort behavior, rather than because the API fundamentally only makes sense with integers. This guideline does not apply to those cases.
 
 NB: This convention is new as of 2024, and most earlier parts of the language do not follow it.
+
+## Reject primitive Strings in iterable-taking APIs and syntax
+
+Any time an iterable value (a value that has a `Symbol.iterator` method) is expected, primitive Strings should be treated as if they were not iterable. Usually, this will mean throwing a `TypeError`. String Objects, however, should be treated like any other Object.
+
+Although primitive Strings are iterable (`String.prototype` has a `Symbol.iterator` method which enumerates code points), it is now considered a mistake to iterate a String without specifying whether the String is providing an abstraction over code units, code points, grapheme clusters, or something else.
+
+NB: This convention is new as of 2024, and most earlier parts of the language do not follow it.