Use of "crappy_ptr" in postfix configuration

gistfile1.txt

pblair@abuse1:/etc/postfix$ cat -n main.cf | grep crappy_ptr -B4 -A5
    50  smtpd_client_restrictions =
    51          #reject_unknown_client,
    52          permit_mynetworks,
    53          reject_unknown_reverse_client_hostname,
    54          check_client_access     regexp:/etc/postfix/crappy_ptr 
    55                                  hash:/etc/postfix/client_access,
    56          sleep 5,
    57          reject_unauth_pipelining


crappy_ptr:
/(a?dsl|dhcp|dyn(amic)?|ppp)?.+?([.-][0-9]{1,3}){4}.+?(a?dsl|dhcp|dyn(amic)?|ppp)?/     REJECT No connection from dynamic space
/(^a?dsl|a?dsl(\.|-)|(\.|-)a?dsl|(\.|-)d(yn|ip|ial)(\.|-)|(\.|-)cable(\.|-)|(\.|-)user(\.|-)|^dynamic|(\.|-)dynamic|dynamic(\.|-)|(\.|-)ppp(oe)?(\.|-|)|^ppp)/  REJECT No connection from dynamic space