meaning if someone makes mostly or even exclusively to that point music that fits into a certain genre (which is just a fluid concept, as this thread well illustrates), that doesn't make them personally that genre or everything they will ever do that genre. so if suddenly a rock band makes a polka song, it's not rock just because their other music is (perceived as) rock. hypothetically, the lack of "purity" in the polka song isn't because it's bringing the rock genre into it but because those particular musicians are bringing themselves, their skills, and their musical interests into what is considered the (more rigidly defined) polka form. to that end, one mustn't get so hung up on the idea of a genre. i think artists perform the music they want to make and others to hear, not genre exercises despite how perfectly it might fit into a preconceived, widely established understanding of the genre. so i would rather listen to what is actually going on in the music than check off a list of what should be found according to the supposed genre.