You shouldn't worry, in the vast majority of cases, we can perform your favorite piece. Not always - we aren't going to attempt the latest rap hit, but in most cases it is already in our repertoire or can be added very conveniently with a small advance notice. We will, of course, work with you in advance to determine any special requests and would certainly point out if something just isn't going to work.
We know that some similar websites list hundreds or even thousands of songs that are available. We do not do that here because all members of An Array of Strings can read music and therefore can be expected to accomodate any reasonable request.