For the full man page, see http://www.purl.org/tcl/home/man/tcl8.5/TclCmd/append.htm

   NAME:  append - Append to variable

   SYNOPSIS:  append varName ?value value value ...?

   DESCRIPTION:   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.

   NOTE:   The append command is a *string* command. If you want to play with lists, definitely use the [concat] or [lappend] commands.

SEE ALSO [concat], [lappend]

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Is the result of an append of two lists a list as you might expect it?
([Peter Lewerin]: Yes, because append is not [lappend].) 
(EE: Erm, NO. The result of an append of two lists is a ''string'', 
which, if it can form a valid list, will shimmer into list form next time it is treated as one.)

 set a [list a b c]
 set b [list 1 2 3]
 append a $b
 puts $a

Note that the third element of this new list is not c, but c1. 
Does anyone know if there are cases where an append would result 
in something '''not''' a list?

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Here's an example of such a case:

 set l1 [list a {b c}]
 set l2 [list {d e} f]
 append l1 $l2
 llength $l1
[RS]: The intended functionality seems to me to be closer to [concat]. 
But if you wish to use ''append'', just add an extra space to separate the parts:
 append l1 " " $l2 
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