The old-style apprenticeship approach to learning how to write songs is being supplemented by university degrees and college diplomas and "rock schools". Knowledge of modern music technology (sequencers, synthesizers, computer sound editing), songwriting elements and business skills are now often requirements for a songwriter. Several music colleges offer songwriting diplomas and degrees with music business modules. Since songwriting and publishing royalties can be substantial sources of income, particularly if a song becomes a hit record; legally, in the US, songs written after 1934 may be copied only by the authors. The legal power to grant these permissions may be bought, sold or transferred. This is governed by international copyright law.