diff --git a/editions/tw5.com/tiddlers/filters/function.tid b/editions/tw5.com/tiddlers/filters/function.tid
index e2e5facc2..4b2a27a22 100644
--- a/editions/tw5.com/tiddlers/filters/function.tid
+++ b/editions/tw5.com/tiddlers/filters/function.tid
@@ -10,7 +10,7 @@ tags: [[Filter Operators]]
 title: function Operator
 type: text/vnd.tiddlywiki
 
-<<.from-version "5.3.0">> The <<.op function>> operator applies a named [[function|Functions]] to the input titles, and returns the results from the function.
+<<.from-version "5.3.0">> The <<.op function>> operator applies a named [[function|Functions]] to the input titles, and returns the results from the function. The function is invoked once with all of the input titles (in contrast, the [[filter Operator]] invokes its function separately for each input title).
 
 The first parameter of the <<.op function>> operator specifies the name of the function to be called. Subsequent parameters are passed to the function.