more robust: resolve historic components via current tool to access current server;
/* Title: Pure/PIDE/document_id.scala
Author: Makarius
Unique identifiers for document structure.
NB: ML ticks forwards > 0, JVM ticks backwards < 0.
*/
package isabelle
object Document_ID
{
type Generic = Long
type Version = Generic
type Command = Generic
type Exec = Generic
val none: Generic = 0
val make: Counter = Counter.make()
def apply(id: Generic): String = Value.Long.apply(id)
def unapply(s: String): Option[Generic] = Value.Long.unapply(s)
}