Explain this code, what happen for field_11 ?? i can not understand this code

 % im2 = binary image;
field_l1 = bwmorph(im2,'thin',inf); 
while(1)
            E_pts=[];
            for i=2:size(field_l1,1)-1
                for j=2:size(field_l1,2)-1
                    if(field_l1(i,j)==1)
                        A=double(field_l1(i-1:i+1,j-1:j+1));
                        if(sum(A(:))==2)
                            E_pts=[E_pts;i j];
                        end
                    end
                end
            end
            
            
            if(isempty(E_pts))
                break
            end

            for i=1:size(E_pts,1)
                curr_pt=E_pts(i,:);
                field_l1(curr_pt(1),curr_pt(2))=0;
                flag=0;
                while(1)
                    pts=[];
                    for j=-1:1
                        for k=-1:1
                            if(field_l1(curr_pt(1)+j,curr_pt(2)+k)==1)
                                pts=[pts;curr_pt(1)+j curr_pt(2)+k];
                            end
                        end
                    end
                    if(isempty(pts))
                        break
                    end
                    if(size(pts,1)>1)
                        break;
                    else
                        curr_pt=pts(1,:);
                        field_l1(curr_pt(1),curr_pt(2))=0;
                    end
                    
%                      figure(3)
%                      imshow(field_l1)
%                      drawnow
%                      pause(0.1)
                end
            end
            
            se=strel('disk',1);
            field_l1=imdilate(field_l1,se);
            field_l1 = bwmorph(field_l1,'thin',inf);
end