var selection = viewer.selection(options);

selection.enable();
selection.disable();
selection.toggleState();

viewer.selection({
    element:                 null, // html element to use for overlay
    showSelectionControl:    true, // show button to toggle selection mode
    toggleButton:            null, // dom element to use as toggle button
    showConfirmDenyButtons:  true,
    styleConfirmDenyButtons: true,
    returnPixelCoordinates:  true,
    keyboardShortcut:        'c', // key to toggle selection mode
    rect:                    null, // initial selection as an OpenSeadragon.SelectionRect object
    allowRotation:           true, // turn selection rotation on or off as needed
    startRotated:            false, // alternative method for drawing the selection; useful for rotated crops
    startRotatedHeight:      0.1, // only used if startRotated=true; value is relative to image height
    restrictToImage:         false, // true = do not allow any part of the selection to be outside the image
    onSelection:             function(rect) {}, // callback
    prefixUrl:               null, // overwrites OpenSeadragon's option
    navImages:               { // overwrites OpenSeadragon's options
        selection: {
            REST:   'selection_rest.png',
            GROUP:  'selection_grouphover.png',
            HOVER:  'selection_hover.png',
            DOWN:   'selection_pressed.png'
        },
        selectionConfirm: {
            REST:   'selection_confirm_rest.png',
            GROUP:  'selection_confirm_grouphover.png',
            HOVER:  'selection_confirm_hover.png',
            DOWN:   'selection_confirm_pressed.png'
        },
        selectionCancel: {
            REST:   'selection_cancel_rest.png',
            GROUP:  'selection_cancel_grouphover.png',
            HOVER:  'selection_cancel_hover.png',
            DOWN:   'selection_cancel_pressed.png'
        },
    },
    borderStyle: { // overwriteable style defaults
        width:      '1px',
        color:      '#fff'
    },
    handleStyle: {
        top:        '50%',
        left:       '50%',
        width:      '6px',
        height:     '6px',
        margin:     '-4px 0 0 -4px',
        background: '#000',
        border:     '1px solid #ccc'
    },
    cornersStyle: {
        width:      '6px',
        height:     '6px',
        background: '#000',
        border:     '1px solid #ccc'
    }
});

- fix behavior when the viewer itself is rotated
- test/fix with multiple images at once

- Now selection can be draw over existing selections, make selection in selection.
To achieve that before you were forced to make a selection outside any other selection and move it over.