[subsection Critcl] The [syscmd critcl] tool is an [emph optional] dependency. [para] It is only required when trying to build the C-based [term accelerators] for a number of packages, as explained in [sectref {Critcl & Accelerators}] [para] Tcllib's build system looks for it in the [variable PATH], using the name [syscmd critcl]. This is for Unix. On Windows on the other hand the search is more complex. First we look for a proper application [syscmd critcl.exe]. When that is not found we look for a combination of interpreter ([syscmd tclkitsh.exe], [syscmd tclsh.exe]) and starkit ([syscmd critcl.kit], [syscmd critcl]) instead. [emph Note] that the choice of starkit can be overriden via the environment variable [variable CRITCL]. [para] Tcllib requires Critcl version 2 or higher. [para] The github repository providing releases of version 2 and higher, and the associated sources, can be found at [uri https://andreas-kupries.github.io/critcl]. [para] Any branch of the repository can be used (if not using the prebuild starkit or starpack), although the use of the stable branch [emph master] is recommended. [para] At the above url is also an explanation on how to build and install Critcl, including a list of its dependencies. [para] Its instructions will not be repeated here. If there are problems with these directions please file a ticket against the [term Critcl] project, and not Tcllib.