The tkined(1) editor distinguishes between various object types. Every object has a unique identifier, called its id, which is used to access and manipulate this object. 

Exchanging the id between tkined(1) and the Tnm extension would be sufficient to implement all of the commands below. However, this would not be very efficient because an application often needs to access a set of standard object attributes. 

To reduce communication costs, an external object representation of the various object types is used which allows caching some information in the Tnm extension.

The external object format is a Tcl list. The first element in this list contains the object type and the second element the id of the object. The following list elements depend on the type of the object as described below.

To extract elements out of the external object format, you should always use one of the ined commands. Although not stated explicitly, all the commands that return information which is included in the external object format accept the external format as a single argument and return the requested value as extracted from the external format. 

By using these commands, you never need to access the external format directly. This makes your scripts usually more readable and makes sure that your scripts continue to work even if the format changes in a future version.