AN ACR LTT AVOIDED A POTENTIAL CONFLICT BY HOLDING SHORT OF A RWY WITHOUT BEING INSTRUCTED TO DO SO.

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WE WERE INITIALLY CLRED BY GND TO 'TAXI TO RWY 34;' NO ADDITIONAL INSTRUCTIONS WERE GIVEN (NOTE: THIS CLRNC IS OFTEN; BUT NOT ALWAYS; ACCOMPANIED BY 'HOLD SHORT OF RWY 29.') APCHING RWY 29; THE CAPT NOTICED A LIGHT ACFT TAXIING INTO POS ON RWY 29. UNSURE OF THAT ACFT'S INTENTIONS; THE CAPT BROUGHT OUR ACFT TO A STOP SHORT OF RWY 29; BUT SLIGHTLY (ABOUT 5 FT) ACROSS THE HOLD SHORT LINE FOR RWY 29. WE CONTACTED GND FOR CLARIFICATION AND WERE TOLD TO 'HOLD SHORT OF RWY 29.' AFTER THE LIGHT ACFT DEPARTED; WE WERE CLRED TO CROSS RWY 29. I QUESTIONED GND CTL; ASKING 'GND; CONFIRM THAT OUR INITIAL CLRNC WAS TAXI TO RWY 34.' HE SAID IT WAS TO 'TAXI TO RWY 34; HOLD SHORT OF RWY 29.' I LET HIM KNOW THAT WE DID NOT RECEIVE THE HOLD SHORT INSTRUCTION. I AM 100 PERCENT CERTAIN THAT THERE WAS NO 'HOLD SHORT' IN OUR ORIGINAL TAXI CLRNC. THE RADIO FREQ WAS NOT CONGESTED AT THE TIME AND I MADE A MENTAL NOTE OF THE OMISSION OF THE 'HOLD SHORT;' AS WE OFTEN RECEIVE THAT CLRNC. I ALSO BASE THIS ON THE REACTION OF THE GND CTLR WHEN WE CONTACTED HIM AFTER OUR STOP SHORT OF RWY 29. HE QUICKLY TOLD US TO 'HOLD SHORT OF RWY 29' AND; WHEN I ADVISED HIM THAT WE WERE SLIGHTLY ACROSS THE HOLD SHORT LINE; HE SEEMED UNCONCERNED. SUPPLEMENTAL INFO FROM ACN 319601: IT'S ALWAYS GOOD PRACTICE TO CLR BOTH WAYS WHILE TAXIING ACROSS A RWY. THIS TIME IT PAID OFF. THIS ALSO COULD HAVE BEEN A READBACK/HEARBACK PROB WITH THE GND CTLR. THE FO READ BACK THE CLRNC 'TAXI TO RWY 34.'