Add note on Creative Commons's enforceability concerns

notes.md

@@ -208,6 +208,23 @@ Licenses](https://creativecommons.org/wp-content/uploads/2018/07/Springing-licen
 
 Lawrence Rosen's book *Open Source Licensing: Software Freedom and Intellectual Property Law* uses the term "eventual source".
 
+# Enforceability
+
+The Creative Commons review seems to have been concerned that springing
+licenses can have enforceability problems.  For their older Founders
+Copyright project, they actually used a copyright assignment to the
+Creative Commons nonprofit rather than (as they usually suggest for
+public licensing of creative works) a unilateral license document.
+
+(Was that because of concerns that copyright can't necessarily be
+abandoned under U.S. law, or because of concerns that a licensor or the
+licensor's heirs could withdraw or revoke the license if it were given
+unilaterally with a delay?)
+
+It might be helpful to understand how serious the enforceability concerns
+are, although it doesn't seem that they've ever been tested in court, so
+it may be hard to say anything definitive.
+
 # Threads where we have posted
 
 Look in the follow-ups in these threads (and subthreads thereof) for