ACR MLG MADE A TKOF AT AZU IN WX RPTED BELOW RWY MINS FOR TKOF.

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AS WE WERE TAXIING OUT TO RWY 17 FOR TKOF; THE TWR GAVE THE NEW ATIS AS 100 OBSCURED; 1/4 MI FOR RWY 17. WE LOOKED AT THE ARPT DIAGRAM PAGE IN THE MANUAL TO CHK WHAT TKOF MIN WERE REQUIRED FOR THAT RWY. IT SHOWED 400-1. EVEN THOUGH IT DIDN'T SAY STD ABOVE THESE NUMBERS; I INTERPRETED THE 1 MI MIN AS STANDARD. WE THEN DECIDED THAT WE COULD GO TO 1/4 MI FOR TKOF WITH ADEQUATE FORWARD VISUAL REF. I DIDN'T THINK THE CEILING LIMITATION WAS BINDING AND I'M STILL NOT SURE. OUR BELIEF WAS CONFIRMED WHEN ANOTHER AIRLINER SAID THAT THEY COULD TKOF UNDER THESE CONDITIONS AND PROCEEDED TO DO SO. WE THEN OBTAINED A TKOF ALTERNATE FROM OUR DISPATCHER AND TOOK OFF FROM RWY 17 AT A20. I'M NOT SURE IF WE BROKE TKOF MINS OR NOT. IF WE DID; WHY DID THE TWR ALLOW PART 121 AND 135 OPERATORS TO USE RWY 17? IS THE CEILING LISTED IN THE TKOF MINS SECTION BINDING? I'VE READ THROUGH THE FARS TO FIND A CLR ANSWER TO THIS AND I'M STILL NOT SURE. I FIGURED I BETTER RPT THIS JUST IN CASE A VIOLATION COMES SNEAKING UP.