Rich text editor accessibility

Keyboard interaction

Key	Action
`Ctrl + B, I or U`	Bold, italic or underline. On Apple devices, ⌘ instead of Ctrl.
`Ctrl + K`	Add or edit a link.
`Ctrl + Alt + 1, 2 or 3`	A heading; Ctrl + Alt + 0 turns it back into a paragraph.
`Ctrl + Shift + 7 or 8`	A numbered or bulleted list.
`Tab and Shift + Tab in a list`	Indent or outdent; elsewhere, Tab leaves the editor.
`Ctrl + Z, Ctrl + Shift + Z`	Undo and redo.
`Left and right arrows in the toolbar`	Move between its buttons.

The content is a textbox with aria-multiline, named by label, with its placeholder in aria-placeholder.
The toolbar is a WAI-ARIA toolbar, one tab stop: formats are toggle buttons with aria-pressed, and each button names its shortcut in aria-keyshortcuts and its tooltip.
A toolbar command sends focus back to the text, and the link dialog returns to it on Escape. Tab never gets stuck: outside lists it leaves the editor.