sub new {
 
    # parameters:
    # [$this],
    # @namedParameters: tree, messageNum, (messageText)
    
    ##### process parameters #####

    my ($this, @namedParameters) = @_;

    # process named parameters (with default values)
    my ($tree, $messageNum, $messageText) = assertNamedParameters([
        numNamedParameters => 3,
        tree => undef,
        messageNum => undef,
        messageText => undef,
        ], \@namedParameters
    );

    # check mandatory paramters
    assertValueIsDefined($this, $tree, $messageNum);