missing button mentioned in documentation

According to the documentation, there is a pin mode playing mode (see http://manual.audacityteam.org/man/playing_and_recording.html for details).
However, in my Audacity I don’t see such button.

Audacity version 2.1.2
OS Ubuntu 14.04

That’s the manual for the current “Audacity 2.1.3” release.

The 2.1.2 manual is available on-line via WayBack Machine.
This is the relevant page: https://web.archive.org/web/20160424004344/http://manual.audacityteam.org/man/playing_and_recording.html
and this is the home page for the 2.1.2 manual: https://web.archive.org/web/20160423185839/http://manual.audacityteam.org:80/index.html