Element interface that allows setting of the TOC.
Elements that support some kind of chapters or editions (or tracks like in the FLAC cue sheet) will implement this interface.
If you just want to retrieve the TOC in your application then all you need to do is watch for TOC messages on your pipeline's bus (or you can perform TOC query). This interface is only for setting TOC data, not for extracting it. To set TOC from the application, find proper tocsetter element and set TOC using Toc.setterSetToc.
Return current TOC the setter uses. The TOC should not be modified without making it writable first.
Get the main Gtk struct
Reset the internal TOC. Elements should call this from within the state-change handler.
Set the given TOC on the setter. Previously set TOC will be unreffed before setting a new one.