Index: Doc/library/imp.rst
===================================================================
--- Doc/library/imp.rst	(revision 62993)
+++ Doc/library/imp.rst	(working copy)
@@ -118,6 +118,12 @@
    be used by import hooks to ensure thread-safety when importing modules. On
    platforms without threads, this function does nothing.
 
+   Once a thread has acquired the import lock, the same thread may acquire it
+   again without blocking; the thread must release it once for each time it has
+   acquired it.
+
+   On platforms without threads, this function does nothing.
+
    .. versionadded:: 2.3