          append varName value ?value value ...?
               Append all of the value arguments to the current  value
               of  variable  varName.  If varName doesn't exist, it is
               given a value equal to the  concatenation  of  all  the
               value  arguments.   This  command provides an efficient
               way to build  up  long  variables  incrementally.   For
               example,  ``append  a  $b'' is much more efficient than
               ``set a $a$b'' if $a is long.
