Colud any one explain me , what the below script does,

My question is what this coomand does "send channel t1 "-workitem oracle_prod01_proxy";


connect rcvcat system/xxxxxx@rman_tst
connect target
run {
allocate channel t1 type 'SBT_TAPE';
send channel t1 "-workitem oracle_prod01_proxy";
backup proxy filesperset 1
(DATABASE format 'df_U%U_1')
;
sql "alter system archive log current";
backup (ARCHIVELOG ALL
format 'df_U%U_1');
backup (CURRENT CONTROLFILE
format 'df_U%U_1');
}