reftex-toc-include-context

reftex-toc-include-context is a variable defined in `reftex-vars.el'.
Its value is

nil

Documentation:
Non-nil means, include context with labels in the *toc* buffer.
Context will only be shown when labels are visible as well.
This flag can be toggled from within the *toc* buffer with the `c' key.

You can customize this variable.