A [Tcl] extension is a [library] of additional commands for a Tcl interpreter.
Extensions are written in [C] using the Tcl [API].  An extension is often included in a [package], where the `[pkgIndex.tcl]` script uses `[load]` to load the extension into the interpreter process. An extension may define new actions, new [widget]s, new processing types, etc.


** See Also **

   [Tcl Extension: User Guide]:   

   [Tcl Extension: Developer Guide]:   

   [Extensions for Tcl and Tk]:   

   [Extending Tcl]:   How to write software that will be implemented as an extension, perhaps in C (or C++ code with `extern "C" {}` around it).

   [Sampleextension]:   

   [package]:   

   [extension language]:   


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