Here’s a nice overview of the changes coming to the WordPress editor in 4.8 from Andrew Ozz. His post includes examples for adding default and custom TinyMCE buttons to the toolbar.
If you’re wondering why TinyMCE was added to the Text Widget, Weston Ruter has the explanation. It’s hard to believe it’s been twelve years since TinyMCE was added to core, but users have had to use raw HTML in their Text widgets.
