diff --git a/docs/apache-airflow/core-concepts/dags.rst b/docs/apache-airflow/core-concepts/dags.rst
index 86f4aaad2eda9..aee35b49e95e4 100644
--- a/docs/apache-airflow/core-concepts/dags.rst
+++ b/docs/apache-airflow/core-concepts/dags.rst
@@ -802,6 +802,10 @@ match any of the patterns would be ignored (under the hood, ``Pattern.search()``
 to match the pattern). Use the ``#`` character to indicate a comment; all characters
 on a line following a ``#`` will be ignored.
 
+As with most regexp matching in Airflow, the regexp engine is ``re2``, which explicitly
+doesn't support many advanced features, please check its
+`documentation <https://github.com/google/re2/wiki/Syntax>`_ for more information.
+
 With the ``glob`` syntax, the patterns work just like those in a ``.gitignore`` file:
 
 * The ``*`` character will any number of characters, except ``/``