Tcl_ParseCommand - function in Tcl's public C API for parsing a
Tcl command from a string.

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Official docs

http://www.purl.org/tcl/home/man/tcl8.4/TclLib/ParseCmd.htm
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  int
  Tcl_ParseCommand(
      Tcl_Interp *interp,
      const char *string,
      int         numBytes,
      int         nested,
      Tcl_Parse  *parsePtr)