diff --git a/website/docs/api/language.jade b/website/docs/api/language.jade
index 9c26f506c..69665ee9d 100644
--- a/website/docs/api/language.jade
+++ b/website/docs/api/language.jade
@@ -111,6 +111,14 @@ p
         +cell -
         +cell A sequence of unicode objects.
 
+    +row
+        +cell #[code as_tuples]
+        +cell bool
+        +cell
+            |  If set to #[code True], inputs should be a sequence of
+            |  #[code (text, context)] tuples. Output will then be a sequence of
+            |  #[code (doc, context)] tuples. Defaults to #[code False].
+
     +row
         +cell #[code n_threads]
         +cell int