This function returns an array of public ids mapped to the specified path PUBLIC and DTDDECL catalog entries. The function returns the number of elements in the array. If first_only is non-zero, then only the first match (if found) is returned. Otherwise, all public ids mapped to the path are returned (the default). If catpath is not specified, then the value of the option catalogpath is used for the list of catalog files to search. Otherwise, catpath specifies an alternate path list to search.