What argument types are expected by rows.setProperty() in the .sdef?

In the scripting dictionary, collections of rows have a .setProperty() function. Could you tell me what type of arguments the functions expects in JavaScript for Automation ?

Context - for example - expanding all outline rows in an outline or set of outline peer rows.

(See, in the Webkit debugger:

Sample code: ( rows.setProperty() arguments apparently not correct here ):

(function () {
    'use strict';

    var oo = Application("com.omnigroup.OmniOutliner4"),
        ds = oo.documents,
        d = ds.length ? ds.at(0) : undefined;

    if (!d) return;

    var rows = d.rows,

        // any expanded element in outline ?
        blnState = rows.expanded().reduce(function (a, e) {
            return a ? a : e;
        }, false);
    rows.setProperty('expanded', !blnState);


For reference, using the .sdef from AppleScript, we might write (to toggle outline expansion)

property pblnState : false

on run {}
    tell application id "com.omnigroup.OmniOutliner4"
        set ds to documents
        if length of ds > 0 then
            set d to item 1 of ds
            return null
        end if
        tell d
            set refRows to a reference to rows
            set expanded of refRows to pblnState
            set pblnState to not pblnState
            return expanded of refRows
        end tell
    end tell
end run

and in osascript JS (JavaScript for Automation), we can batch get the values of the .expanded() state by writing:

// --> [true, true, true, false, false, false, true, false, false]

and set the value of an isolated row by using the single row object row.setProperty()

rows.at(0).setProperty('expanded', !blnState);

The question is the syntax of the method call for a plural rows collection - the equivalent of the AppleScript:

set expanded of refRows to pblnState