I need to add a static block of text above the editor. This needs to appear not only on post edit screens, but also the widgets screen, as I'm using a plugin to enable usage of the visual editor there as well.
On post edit screens, the filters
edit_form_after_title work ok, the placement isn't ideal, but neither of them work on the widget screen, so they're not usable.
The only filter I've found that actually applies to the editor itself is
tiny_mce_before_init but I'm not sure how I could use that to just add static text.