This identifier reports the type of the caller, not the call method. So when you call it from the editbox, it reports the caller as the editbox. When it is called via a DLL, it reports a DLL. If it is called from a command, it reports a command. And so on.

Code:
tc {
  echo caller: $caller
  tc1
  noop $tc1
}
tc1 {
  echo caller: $caller
  echo isid: $isid
}