b3270 passthru Indication

### passthru Indication

A registered pass-through action has been invoked.

Attribute | Always present? | Purpose
--- | --- | ---
p-tag | yes | Emulator-generated tag
parent-r-tag | no | UI-generated tag of parent
action | yes | Action name
arg1 | no | First argument
argn | no | Last argument

The UI must respond to this indicatation with a suceed or fail operation, passing back in the same p-tag value to identify this particular invocation.

If the action was invoked by the UI (through the run operation), directly or indirectly, the parent-r-tag will indicate the r-tag passed to run.

Example:

    <passthru p-tag="ui-1234" action="NewKeymap" arg1="special" arg2="foo"/>

b3270: Protocol - Operations - Indications