squid src/Makefile options

Hello,
can anybody tell me where are options in src/Makefile descrbed what they
exactly do ?
I didn't find it in docs :(

I mean these:
HOST_OPT = # -DCACHEMGR_HOSTNAME="getfullhostname()"
AUTH_OPT = # -DUSE_PROXY_AUTH=1
LOG_HDRS_OPT = # -DLOG_FULL_HEADERS=1
ICMP_OPT = # -DUSE_ICMP=1
DELAY_HACK = # -DDELAY_HACK=1
USERAGENT_OPT = # -DUSE_USERAGENT_LOG=1
KILL_PARENT_OPT = # -DKILL_PARENT_OPT
USE_POLL_OPT = # -DUSE_POLL
# do NOT define both USE_SPLAY_TREE and USE_BIN_TREE at the same time!
USE_SPLAY_TREE = # -DUSE_SPLAY_TREE
USE_BIN_TREE = # -DUSE_BIN_TREE
RELOAD_INTO_IMS = # -DRELOAD_INTO_IMS
UNDERSCORES_OPT = # -DALLOW_HOSTNAME_UNDERSCORES

-- 
 Matus "fantomas" Uhlar, network manager at faculty of civil engineering
 of Technical University in Kosice, Slovakia
 E-mail: [email protected] ; WWW: http://ccsun.tuke.sk/users/uhlar