Add FIXME comment

src/aggregrate-errors.js

@@ -11,6 +11,7 @@ const { dim, dimBold, highlight, highlightBold } = require("./colors");
 
 // TODO: Omit the "At (root)" for path-less errors, to avoid confusion when singular values are being compared?
 // TODO: Move out the path generating logic into a separate module, to better support custom error formatting code
+// FIXME: Remove duplicate subError-less error messages, when heuristics are enabled? eg. multiple "Must be an array" for different arrayOf combinators
 
 function joinPathSegments(segments) {
 	return (segments.length > 0)