The Apple Podcasts docs say that `itunes:explicit` should be either `true` or `false` but it doesn't accept either of those values. Only `yes` or `no` cause the markers to appear.
URL. The URL attribute points to your podcast media file. The file extension specified within the URL attribute determines whether or not content appears in the podcast directory. Supported file formats include M4A, MP3, MOV, MP4, M4V, and PDFPDF.
