Function $document->setTitle($title) is called from “administrator/components/com_virtuemart/classes/mainframe.class.php”:

function setPageTitle( $title ) {
    global $mainframe;
    $title = strip_tags(str_replace(' ',' ', $title));
    $title = trim($title);
    if( defined( '_VM_IS_BACKEND')) {
        echo vmCommonHTML::scriptTag('', "//<![CDATA[
        var vm_page_title=\"".str_replace('"', '\"', $title )."\";
        try{ parent.document.title = vm_page_title; } catch(e) { document.title =vm_page_title; } 
        //]]>
        ");
        
    }
    elseif( vmIsJoomla('1.5') ) {
        $document=& JFactory::getDocument();
        $document->setTitle($title);
    } else {
        $mainframe->setPageTitle( $title );
    }
}

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I did some investigation of VirtueMart 1.1.x discount system and the first thing I did notice is that VirtueMart 1.1.x does not support progressive discounts natively. In other words it does not allow to define the discount based on the amount of products bought or total amount of money paid.

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