package Err;
use base qw( Exporter );
use Carp qw( croak );
my( %defaults, @options );
BEGIN {
    %defaults= (
        Title => 'An error has occurred',
        Message => 'If error persists, seek assistance',
    );
    @options= keys(%defaults);
}
sub new {
    my $this= shift;        # Either a package name or an object.
    croak 'Usage: $handle= ',__PACKAGE__,"->new();\n",
          '   or: $handle= $ErrHandle->new()',"\n"
        if  @ARGV;
    my $class= ref($this) || $this;
    # Copy defaults from calling object or use standard defaults:
    my $obj= ref($this) ? {%$this} : {%defaults};
    return bless $obj, $class;
}
sub import {
    # Export a unique $ErrHandle to each caller:
    my $uniq= $_[0]->new();
    *ErrHandle= \$uniq;
    goto &Exporter::import;
}
sub Configure {
    my( $self, $opts )= @_;
    croak 'Usage: $ErrHandle->Configure( ',
          '{ Title=>"new title", Message=>"new msg" } )', "\n"
        unless  2 == @ARGV  &&  ref($opts)
          &&  UNIVERSAL::isa($opts,"HASH");
    my @err= grep { ! exists $defaults{$_} } keys %$opts;
    croak __PACKAGE__,"::Configure: Unknown option(s) ",
          "(@err) not (@options)\n"
        if  @err;
    @{$self}{keys %$opts}= values %$opts;
    return $self;
}