added a tip for the block tag

diff --git a/doc/functions/block.rst b/doc/functions/block.rst
index fd571ef..b7df6d8 100644 (file)
--- a/doc/functions/block.rst
+++ b/doc/functions/block.rst
@@ -12,4 +12,10 @@ times, use the ``block`` function:
 
     {% block body %}{% endblock %}
 
+.. tip::
+
+    Block names must only contain letters, numbers, and underscores (``_``).
+    The internal regexp reads as follows:
+    ``[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*``.
+
 .. seealso:: :doc:`extends<../tags/extends>`, :doc:`parent<../functions/parent>`