$delim = 'A -3 C -4 B';
$array = 
     ['A -4 A','A -1 C','C -4 D','D -4 B','B -3 C','C -2 B','B -1 E'];
            +   *    +   *    +   *    +   *    +   *    +   *

# Note that in $array,  starting from 
# second element $array->[1] until $array->[-1], 
# the first alphabet  ( asterisks *)  is  actually 
# a repeat of the last alphabet ( plus +) 
# from the previous element.

##</code><code>##

my $delim       = 'A -3 C -4 B';
my $delim_reg   = ['A -3 C','C -4 B'];

##</code><code>##

my $delim_reg   = ['A -3 C','C -4 B'];

                    \__i__/  \__j__/ --> sub-regions


my $array   =  
   ['A -4 A','A -1 C','C -4 D','D -4 B','B -3 C',  'C -2 B','B -1 E'];
                 
     |\_____i_______/                              \__j__/|-> Inst 1
     |____________________________________________________|


             |\_i__/  \_____j________/ |-------> Instance 2
             |_________________________|
                          
                         ... till
                          

    |\_____i_______/  \_______________j__________________/ |--> Inst 6
    |______________________________________________________|


##</code><code>##

my $VAR =  [ 

[['A -4 A', 'A -1 C'], ['C -2 B']],                            # Ins1
[['A -4 A', 'A -1 C'], ['C -4 D','D -4 B']],                   # Ins2
[['A -4 A', 'A -1 C'], ['C -4 D','D -4 B','B -4 C','C -2 B']], # Ins3
[['A -4 A', 'A -1 C', 'C -4 D','D -4 B','B -4 C'],['C -2 B']], # Ins4
[['A -1 C'], ['C -4 D', 'D -4 B']],                            # Ins5
[['A -1 C'], ['C -4 D', 'D -4 B','B -3 C','C -2 B']],          # Ins6

]

##</code><code>##

use Data::Dumper;
my $delim   = 'A -3 C -4 B';
my $array   =  
     ['A -4 A','A -1 C','C -4 D','D -4 B','B -3 C','C -2 B','B -1 E'];

get_delim_region($delim,$array);

sub get_delim_region{

    my ($delim,$array)	= @_;
    my $delim_reg = decomp_str($delim);

    # I'm really stuck from here.....

    my @instances;
   
    OUT:
    foreach  my $delim_rg ( @{$delim_reg}  ){
        my @delimreg;
        my $st1 = (split(" ",$delim_rg))[0];
        my $st2 = (split(" ",$delim_rg))[2];
 
        IN:
        foreach  my $i ( 0 ..  @{$array}-1  ){
            my $tr1 = (split(" ",$array->[$i]))[0];
            my $tr2 = (split(" ",$array->[$i]))[2];

            if($st1 eq $tr1){
                push @delimreg,$array->[$i];
            }
            elsif($st2 eq $tr2){
                push @delimreg,$array->[$i];
                next OUT; 
            }
            push @instances, [ @delimreg ]; 
        }     
     }
      print Dumper \@instances;
      return ;
}	

sub decomp_str{

    # This subroutine decompose a string into sub-regions i.e
    # from:  $delim       = 'A -3 C -4 B';
    # into:  $delim_reg   = ['A -3 C','C -4 B'];

    # Credit Roy Johnson - fastest

    [$_[0] =~ /(?=([a-z]\s*(?:\S+\s*){2}))\S+\s*/gi ]
}