This question is about Xonotic.
Can someone explain what that code does exactly and why it is not done by excluding servers from listing, instead relying on some clientside hax

qcsrc/menu/xonotic/serverlist.qc, line 540
// server banning
n = tokenizebyseparator(_Nex_ExtResponseSystem_BannedServers, " ");
for(i = 0; i < n; ++i)
if(argv(i) != "")
sethostcachemaskstring(++m, SLIST_FIELD_CNAME, argv(i), SLIST_TEST_NOTSTARTSWITH);