do_initialization() example

Dear Fellow Erlangers,
In proc_lib module this example includes a function in the case
statement;

	-module(my_proc). -export([start_link/0]). -export([init/1]).
start_link() -> proc_lib:start_link(my_proc, init, [self()]).
init(Parent) -> case do_initialization() of ok ->
proc_lib:init_ack(Parent, {ok, self()}); {error, Reason} ->
exit(Reason) end, loop().

could someone kindly direct me to an example of a

do_initialization()

function?

thank you in advance,

Peter