lappend varName ?value value ...?
Appends each value to the end of the list stored in varName. (From the Tcl/Tk Reference Guide)
lappend is the only list-command which requires the name of the list rather than the list itself.
lappend listName
rather than
lappend $listName
This command differs from append in that values are appended as list elements rather than raw text.
lappend will not make varName a list ; if it is one before the command, it will continue to be one.
You do not need to assign the results of lappend to varName; lappend modifies varName directly.