This command, a part of tclx is documented thusly within the package:
ctoken strvar separators Parse a token out of a character string. The string to parse is contained in the variable named strvar. The string separators contains all of the valid separator characters for tokens in the string. All leading separators are skipped and the first token is returned. The variable strvar will be modified to contain the remainder of the string following the token. This command does not work with binary data. This command is provided by Extended Tcl.
Can anyone provide me an example of how this works?