diff --git a/vim/xdebug.md b/vim/xdebug.md
index a55710e..cb5b99d 100644
--- a/vim/xdebug.md
+++ b/vim/xdebug.md
@@ -48,6 +48,17 @@ php -r 'xdebug_info();'
 ```
 ### Trigger
 
+
+Xdebug will initiate a debug session in the presence of the XDEBUG_SESSION HTTP cookie.
+
+You can pick any value for the cookie, unless xdebug.trigger_value is set.
+
+A typical header looks like:
+
+```
+Cookie: XDEBUG_SESSION=start
+```
+
 To signal the debugger to initiate connections, Xdebug will look whether the XDEBUG_SESSION environment variable is present.
 
 ```