The result of Tcl_InitSubsystems is the full Tcl version with build information (e.g., 9.0.0+abcdef...abcdef.gcc-1002).
Tcl_InitSubsystems is very similar in use to Tcl_FindExecutable. It can be used when Tcl is used as utility library, no other encodings than utf-8, iso8859-1 or utf-16 are used, and no interest exists in the value of info nameofexecutable. The system encoding will not be extracted from the environment, but falls back to utf-8.