sub validateOptions {
    my( $hvOptions, $hvUserOpts )= @_;
    for my $key (  keys %$hvOptions  ) {
        $hvOptions->{$key}= delete $hvUserOpts->{$key}
            if  exists $hvUserOpts->{$key};
    }
    if(  %$hvUserOpts  ) {
        my $subName= (caller(1))[3];
        croak "$subName: Invalid options (",
            join(",",keys %$hvUserOpts),")";
    }
    return $hvOptions;
}


BEGIN {
    my %defaults= ( Access=>READ_ONLY, Delimiter=>"/" );
    sub Open {
        my( $keyName, $hvUserOpts )= @_;
        my $hvOpts= validOptions( {%defaults}, $hvUserOpts );
        # ...
    }
}

BEGIN {
    my %defaults= ( Delimiter=>"/", Translate=>"text" );
    sub Read {
        my( $handle, $hvUserOpts )= @_;
        my $hvOpts= validOptions( {%defaults}, $hvUserOpts );
        # ...
    }
}