sub PutEnvelope {
        # store "ignored" outer tag for later use by puttag
        my $self = shift;
        my $tref = shift;
        my $envtag = keys %$tref;
        my $depth = 1;
        my $eref = ( ( $self -> { ENVELOPE } ) ||= {} );
        for ( ;( $depth < ( $self -> { THIS }{ DEPTH } ) ); $depth++ ) {
                my $k = ( keys %$eref ) || $;;
                $eref = ( $eref -> { $k }{ SUBTAGS }[0] ||= undef() );

        }
        $eref -> { $envtag } ||= ( $eref -> { $; } ||= undef()  );
        $eref -> { $envtag }{ ASSMNTS } = $tref -> { ASSMNTS }; # envelope tags must preserve assignments
        delete $eref -> { $; }; # replace any $; at same level.
}