How does Qualtrics randomly select users to fulfil sampling criteria?

what logic is followed in the actual sample selection?
In our Exit Survey set up, we currently have an Action Set that specifies the Intercept to be triggered when a user leaves any one of a long list of urls. The logic being to trigger the Intercept if user leaves URL A or URL B or URL C (etc). Within that Action Set we have the sampling rate set to 10%.
Please can you advise if Qualtrics assigns that 10% to the entire set of URLS taken together or if it assigns that 10% to each individual URL. In other words is it: IF USER LEAVES (URL A OR URL B OR URL C) THEN APPLY 10% SAMPLING RATE TO COMBINED POPULATION OF USERS WHO HAVE VISITED (URL A AND URL B AND URL C)
 Or is it
 (IF USER LEAVES URL A THEN APPLY 10% SAMPLING RATE TO THE POPULATION OF USERS WHO HAVE VISITED URL A) OR (IF USER LEAVES URL B THEN APPLY 10% SAMPLING RATE TO POPULATION OF USERS WHO HAVE VISITED URL B), OR (IF USER LEAVES URL C THEN APPLY 10% SAMPLING RATE TO POPULATION OF USERS WHO HAVE VISITED URL C)