Optional ReadonlyattrsExtra attributes on the decorated span, data- keys for a feature to
recognise its own spans by, title, role.
A decoration that can only set a class name can be seen but not identified: the painted span carries nothing linking it back to whatever produced it, so a hover card or a click menu has no way to know which of a block's decorations the pointer is over.
ReadonlyclassReadonlyfromOptional ReadonlystyleExtra inline CSS on the decorated span (a per-range highlight colour, …).
ReadonlytoOptional ReadonlywidgetZero-width widget rendered at from (requires from === to), e.g. a
marker pinned to one position. The element is wrapped in a non-editable
span the position mapper skips.
An inline range in a textblock rendered with an extra class (search match, …).