cconcat is one of many [Tclx commands].

===
     cconcat ?string1? ?string2? ?...?
          Concatenate the arguments, returning the resulting string.
          While string concatenation is normally performed by the
          parser, it is occasionally useful to have a command that
          returns a string.  The is generally useful when a command to
          evaluate is required.  No separators are inserted between
          the strings.

          This command is UTF-aware.
===

A minimal [pure-Tcl] substitute would be
 proc cconcat args {join $args ""} ;# RS

See also [string concat] for contemplations about adding this functionality as a subcommand of [string].
----
!!!!!!
%| [Category Command], a part of the [Tclx] package |%
!!!!!!