function _popup_( url, width, height )
{
    width = width || '80%';
    height = height || '70%';

    if ( typeof width == 'string' && width.length > 1 && width.substr( width.length - 1, 1 ) == '%' )
        width = parseInt( window.screen.width * parseInt( width, 10 ) / 100, 10 );

    if ( typeof height == 'string' && height.length > 1 && height.substr( height.length - 1, 1 ) == '%' )
        height = parseInt( window.screen.height * parseInt( height, 10 ) / 100, 10 );

    if ( width < 100 )
        width = 100;

    if ( height < 100 )
        height = 100;

    var top = parseInt( ( window.screen.height - height ) / 2, 10 ),
        left = parseInt( ( window.screen.width  - width ) / 2, 10 ),
        options = 'location=no,menubar=no,toolbar=no,dependent=yes,minimizable=no,modal=yes,alwaysRaised=yes,resizable=yes' +
        ',width='  + width +
        ',height=' + height +
        ',top='  + top +
        ',left=' + left;

    var popupWindow = window.open( '', null, options, true );

    // Blocked by a popup blocker.
    if ( !popupWindow )
        return false;

    try
    {
        popupWindow.moveTo( left, top );
        popupWindow.resizeTo( width, height );
        popupWindow.focus();
        popupWindow.location.href = url;
    }
    catch (e)
    {
        popupWindow = window.open( url, null, options, true );
    }

    return true ;
}