import QtQuick 2.2
Rectangle
{
    id: root;
    default property alias contents: contentFrame.children;
    color: "#05f"; width: 100; height: 100;

    Rectangle
    {
        id: contentFrame;
        anchors
        {
            fill: parent;
            leftMargin: 10; topMargin: 10; rightMargin: 10; bottomMargin: 10;
        }
        color: "#888";
    }
}

import QtQuick 2.2

Test1
{
    id: root;

    Rectangle
    {
        id: contentFrame;
        anchors
        {
            fill: parent;  // Note that this is NOT root, but Test1's default item!
            leftMargin: 10; topMargin: 10; rightMargin: 10; bottomMargin: 10;
        }
        color: "#0a0";
    }

    /* Component // CRASH if you uncomment this!
    {
        id: separator;
        Rectangle
        {
            height: 1;
            color: "#fab";
        }
    } */
}