Hi -
What nice idea (building an API/SDK around Spotify web)! I wonder if you've also exposed enough low-level detail to invoke useful features like "play again from 15 seconds ago" and actual looping of a predefined section?
Best way to describe the song looping is in this unrealized, fairly popular Spotify feature request:
https://community.spotify.com/t5/Closed-Ideas/Music-Looping-individual-Songs-or-Parts/idi-p/1551156