Custom Web Player for Spotify

As far as I know, it is not possible to create a web app (outside of spotify.com) providing a custom web player that plays Spotify songs, right? The only option is apparently the play button, which is very limited.

I just saw, however, this example

1) http://static.echonest.com/enspex/web/ChillRadio/

this

2) http://lab.possan.se/thirtify/

and this one

3) https://developer.spotify.com/web-api/code-examples/ (see "Play Anything" snippet)

which seems to use custom player (2) and 3) doesn't work for me though). Is there any document not documented?

thank