read-special in readable-snip<%>

• (send a-readable-snip read-special source line column position) -> an arbitrary value
     source : value
     line : exact non-negative integer or #f
   column : exact non-negative integer or #f
   position : exact non-negative integer or #f

  The arguments are the same as the arguments to a procedure returned by a custom input port's read-proc; see Custom Ports, section 11.1.7 in PLT MzScheme: Language Manual for details. The result is also the same as the result from a read-proc-produced procedure.