1. A method of designing customized items comprising: a. receiving from a web server a web page containing (i) a design document encoding graphic elements having properties, (ii) a first server-rendered composite image of an item bearing a design characterized by the graphic elements, and (iii) a form for sending properties of the graphic elements to the web server, the form targeting a defined area of the web page; b. displaying the web page using a display device; c. receiving edits to the properties of the graphic elements; d. sending a modified design document to the web server using the form, the modified design document including (i) data that reflect the received edits and (ii) all image state information necessary to render a composite image; e. receiving a second server-rendered composite image of the item from the web server, the second server-rendered composite image having been rendered using the sent modified design document; and f. displaying the second server-rendered composite image of the item in the area of the web page targeted by the form.