http://www.tcl.tk/man/tcl8.6/TclCmd/transchan.htm 

This is a protocol for defining a '''channel transform''', which is a way to intercept the reading and writing of bytes on a channel with a Tcl script and modify them (e.g., handling encryption, logging or compression). The script is attached via [chan push].

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The script is defined by a ''command prefix'' (which could be the name of an ensemble command, an [TclOO%|%object], or even a multi-word [apply%|%lambda term]). We'll treat it as an object here.

When attached, the '''initialize''' method is called to get the list of supported methods (by name). For a reader transform, the relevant methods are '''read''' (mandatory for readers), '''drain''' and '''limit?'''. For a writer transform, the relevant methods are '''write''' (mandatory) and '''flush'''. Both types must also support '''finalize''' (for when the channel is closed or the transform detached with [chan pop]) and may support '''clear''' too.


[[replace with details of this command]]

[[[DKF]: It's not a command; it's a protocol that a command prefix should adhere to to participate as a [chan push%|%channel transform].]]

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