All 
Publication                            Resources that are hyperlinked to from Publication Resources in the                             
spine                         must themselves be listed in the 
spine, where                        hyperlinking is defined to be any linking mechanism that requires the 
User to navigate away from the current resource. Common                        hyperlinking mechanisms include the 
href attribute of the 
[HTML]                         a and 
area elements and scripted links (e.g., using DOM Events and/or form                        elements). The requirement to list hyperlinked resources applies recursively (i.e., all Publication                        Resources hyperlinked from hyperlinked Publication Resources also have to be listed, and so                        on.).