diff --git a/doc/foot.ini.5.scd b/doc/foot.ini.5.scd
index 24df3cbb..083a1087 100644
--- a/doc/foot.ini.5.scd
+++ b/doc/foot.ini.5.scd
@@ -1031,6 +1031,21 @@ can configure the background transparency with the _alpha_ option.
 	Background translucency. A value in the range 0.0-1.0, where 0.0
 	means completely transparent, and 1.0 is opaque. Default: _1.0_.
 
+*alpha-mode*
+	Specifies when *alpha* is applied. One of *default*, *matching* or
+	*all*.
+	
+	*default* applies *alpha* to cells with the default background
+	color, excluding cells with the same RGB value as the default
+	background color.
+	
+	*matching* is the same as *default*, but also applies *alpha* to
+	cells with the same RGB value as the default background color.
+	
+	*all* applies *alpha* to all cells, regardless of background color.
+	
+	Default: _default_
+
 *selection-foreground*, *selection-background*
 	Foreground (text) and background color to use in selected
 	text. Note that *both* options must be set, or the default will be