diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 79c5409..bd05691 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2554,6 +2554,7 @@
 popup_filter_yesno({id}, {key}) Number	filter for a dialog popup window
 popup_getoptions({id})		Dict	get options of popup window {id}
 popup_getpos({id})		Dict	get position of popup window {id}
+popup_getpreview()		Number	get window ID of preview popup window
 popup_hide({id})		none	hide popup menu {id}
 popup_menu({what}, {options})	Number	create a popup window used as a menu
 popup_move({id}, {options})	none	set position of popup window {id}