Code mode

the purpose of the code button is absolutely unclear. In other editors, this is editing the html code of the edited text. What is the essence of this mode in your editor?

Start by locating the Code mode button and inspecting its current behavior in the Trix editor. Compare that behavior with the expectation described in the issue, then determine whether the purpose should be clarified in the interface, documentation, or both. Done means a newcomer can understand what Code mode does.

Written by the indexing model from the issue text.