Clarifying nonlocal doc: SyntaxError is raised if nearest enclosing scope is global

Doc/reference/executionmodel.rst

@@ -139,8 +139,9 @@ namespace.  Names are resolved in the top-level namespace by searching the
 global namespace, i.e. the namespace of the module containing the code block,
 and the builtins namespace, the namespace of the module :mod:`builtins`.  The
 global namespace is searched first.  If the names are not found there, the
-builtins namespace is searched.  The :keyword:`!global` statement must precede
-all uses of the listed names.
+builtins namespace is searched next. If the names are also not found in the
+builtins namespace, new variables are created in the global namespace.
+The global statement must precede all uses of the listed names.
 
 The :keyword:`global` statement has the same scope as a name binding operation
 in the same block.  If the nearest enclosing scope for a free variable contains