PLT MISINTERPRETS ATC CLRNC AND BEGINS DSCNT BEFORE CLRED.

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PERCEIVED CLRNC 'CLRED DIRECT HOAG1; COAST 2 ARR; DSND VIA THE COAST 2.' WHEN RPTING OUT OF 15000 FT FOR 10000 FT WE WERE TOLD 'OK; BUT YOU WERE NOT CLRED TO DSND; ONLY TO FLY THE RTE; DSND NOW VIA THE COAST 2.' WE HAD ALREADY DSNDED TO 14500 FT WHEN THE 'OFFICIAL' CLRNC WAS GIVEN. I ASKED AND CTR ADVISED OF NO CONFLICT. AN OPINION: ATC NEEDS TO STANDARDIZE VERBIAGE REGARDING DSCNT CLRNC ASSOCIATED WITH FMS ARRS. EXAMPLE: IAH DSCNT CLRNC -- 'CLRED VIA THE COAST 2; DSND VIA THE COAST 2.' HOWEVER; AT SNA THE CLRNC 'CLRED FOR THE SNA E SIDE 1 ARR' INCLUDES CHANGES IN ALT. THE ONLY WAY FOR PLTS TO KNOW IS TO ASK. WE DO; AND THEIR RESPONSE IS ALWAYS THE SAME 'OF COURSE;' OR 'YES.' BECAUSE OF THIS WE ASK ON EVERY FMS ARR IF WE ARE CLRED FOR THE VERT PORTION. THE ONLY CITY I AM AWARE OF WHICH SPECIFICALLY STATES CLRNC FOR DSCNT IS IAH WITH THEIR 'CLRED TO DSND VIA THE COAST 2.' ADDITIONALLY; IT IS MY BELIEF THAT EVERY ARR CLRNC INCLUDES ALT; BUT THIS IS NOT DONE. EXAMPLE: 'CLRED FOR THE DAS 2 ARR MAINTAIN (FL370/OR PD X000 FT). THE ONLY TIME I PERCEIVE A PROB IS ASSOCIATED WITH THE FMS ARR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE WAS FLYING A B737-300. HE STATED THAT BOTH THE E SIDE 1 AT SNA AND THE COAST 2 AT IAH ARE FMS ARRS.