A TECHNICAL RWY INCURSION RWY 21 WHEN A B737 PIC TAXIES ACROSS THE 'RWY APCH' LINES ON TXWY E AT ABQ.

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CLRED TO TAXI FROM RAMP TO RWY 21. INSTRUCTIONS WERE 'TAXI RWY 21 VIA TXWY C AND TXWY E; HOLD SHORT OF RWY 8/27.' AFTER HOLDING FOR LNDG ACFT; 'CLRED TO CROSS RWY 8/26.' THERE ARE NO RWY HOLD LINES FOR RWY 21 ON TXWY E. I WAS NOT INSTRUCTED TO HOLD SHORT OF RWY 21 APCH; SO I TAXIED ACROSS THIS LINE. AFTER I CROSSED; WE REALIZED THAT TXWY E DOES NOT CROSS THE RWY; BUT PASSES THE END OF RWY 21 (ON THE N END). ALTHOUGH THE CHART WAS OUT AND I WAS USING IT; I WAS LOOKING FOR A 'RWY HOLD' LINE WHICH DOESN'T EXIST. I WOUND UP TAXIING ON TXWY E ALMOST PAST THE RWY BEFORE I COULD SEE IT ACROSS COCKPIT ON MY R. THERE WAS NO ACFT ON APCH TO RWY 21 AND NO CONFLICT CREATED. HOWEVER; I FEEL THAT IN THIS SIT AT ABQ THAT THE CTLR SHOULD SPECIFY TO EITHER 'TAXI INTO POS RWY 21' OR TO 'HOLD SHORT OF RWY 21 APCH.' TECHNICALLY; I DON'T THINK WE VIOLATED OR ENCROACHED THE RWY SINCE WE WERE ON TXWY E; BUT IT WAS A VERY UNCOMFORTABLE FEELING. THE CTLR SAID IT WAS 'NO PROB;' BUT BETTER TERMINOLOGY COULD HAVE CLARIFIED THE CTLR'S WISH AND AVOIDED A POTENTIALLY DANGEROUS SIT (HAD AN ACFT BEEN ON APCH TO RWY 21). IT IS MY UNDERSTANDING THAT THERE IS NO REQUIREMENT TO HOLD SHORT OF RWY APCH LINES UNLESS INSTRUCTED TO DO SO BY GND CTL.