- If the value of this element is a number, it defines the index of the search
 path entries from the resource resolver. The defined search path is used as
 a prefix to mount this servlet. The number can be -1 which always points to the
 last search entry. If the specified value is higher than than the highest index
 of the search paths, the last entry is used. The index starts with 0.
 If the value of this property is a string and parseable as a number, the above
 logic is used.
 
 - If the value of this element is a string starting with "/", this value is applied
 as a prefix, regardless of the configured search paths!
 
 - If the value is anything else, it is ignored.
 
 
 If this property is empty, the configuration of the 
org.apache.sling.servlets.resolver.internal.SlingServletResolver
 service is used.
 In case even that one is not set "/" is used as prefix.