Refer to vmod-j

src/vmod_frozen.vcc

@@ -173,6 +173,12 @@ For JSON ``null`` values, the `null` argument is returned.
 For paths which are not found and not defined as required, the `undef`
 argument is returned.
 
+.. _vmod-j: https://gitlab.com/uplex/varnish/libvmod-j
+
+JSON strings are returned literally as found in the input string,
+without the enclosing quotes. To unescape them to UTF-8, the
+``j.unescape()`` function from `vmod-j`_ can be used.
+
 $Method STRING .type(STRING path)
 
 Return the JSON type of an extracted path or NULL otherwise.