diff --git a/changelog/3549.doc.rst b/changelog/3549.doc.rst
new file mode 100644
index 000000000..62bc4f9a5
--- /dev/null
+++ b/changelog/3549.doc.rst
@@ -0,0 +1 @@
+Add documentation for the ``--strict`` flag.
diff --git a/doc/en/mark.rst b/doc/en/mark.rst
index e48135b10..e47b8c3fb 100644
--- a/doc/en/mark.rst
+++ b/doc/en/mark.rst
@@ -26,10 +26,30 @@ which also serve as documentation.
     :ref:`fixtures <fixtures>`.
 
 
-.. currentmodule:: _pytest.mark.structures
-.. autoclass:: Mark
-    :members:
-    :noindex:
+Raising errors on unknown marks: --strict
+-----------------------------------------
+
+When the ``--strict`` command-line flag is passed, any marks not registered in the ``pytest.ini`` file will trigger an error.
+
+Marks can be registered like this:
+
+.. code-block:: ini
+
+    [pytest]
+    markers =
+        slow
+        serial
+
+This can be used to prevent users mistyping mark names by accident. Test suites that want to enforce this
+should add ``--strict`` to ``addopts``:
+
+.. code-block:: ini
+
+    [pytest]
+    addopts = --strict
+    markers =
+        slow
+        serial
 
 
 .. `marker-iteration`