Since damage to text witnesses frequently makes them harder to
    read, the 
damage element will often contain an
    
unclear element.  If the damaged area is not continuous
    (e.g. a stain affecting several strings of text), the
    
group attribute may be used to group together several
    related 
damage elements; alternatively the 
join
    element may be used to indicate which 
damage and
    
unclear elements are part of the same physical
    phenomenon.