restrictTranslate - restrict the translation (movement) of elements by a given bouding box. If set to true, the user will not be able to move elements outside the boundary of the paper area. It's set to false by default. This option also accepts a function with signature function(elementView) in which case it must return a bounding box (an object of the form { x: Number, y: Number, width: Number, height: Number }) that defines the area in which the element represented by elementView can be moved. For example, to restrict translatoin of embedded elements by the bounding box defined by their parent element, you can do:

restrictTranslate: function(elementView) {
    var parentId = elementView.model.get('parent');
    return parentId && this.model.getCell(parentId).getBBox();
}