diff --git a/iframes.md b/iframes.md
index abb22543b..4135067ba 100644
--- a/iframes.md
+++ b/iframes.md
@@ -1,6 +1,9 @@
 # iframes
 
 - An [[iframe]] is an easy way to implement [[transclusion]].
+- Web content embedded this way must allow it using either [[x-frame]] or [[content security policy]].
+  - https://support.mozilla.org/en-US/kb/xframe-neterror-page?as=u&utm_source=inproduct
+- See also [[embed]].
 
 
 [//begin]: # "Autogenerated link references for markdown compatibility"
diff --git a/x-frame.md b/x-frame.md
new file mode 100644
index 000000000..26885245a
--- /dev/null
+++ b/x-frame.md
@@ -0,0 +1,11 @@
+# x-frame
+
+- a [[http header]]
+  - [[pull]] [[x-frame-options]]
+  - [[go]] https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options
+  - Controls [[HTTP]] permissions for [[frame]], [[iframe]], [[embed]], [[object]].
+
+[//begin]: # "Autogenerated link references for markdown compatibility"
+[pull]: pull "Pull"
+[go]: go "Go"
+[//end]: # "Autogenerated link references"
\ No newline at end of file