Add notice in documentation about yr_rules_scan_XXXX functions not being re-entrant.
@@ -278,6 +278,9 @@ single match for the string, even if it appears multiple times in the scanned
data. This flag has the same effect of the ``-f`` command-line option described
in :ref:`command-line`.
+Notice that you shouldn't call any of the ``yr_rules_scan_XXXX`` functions from
+within the callback as those functions are not re-entrant.
+
Using a scanner
---------------
