'heading' as first/default option

[panpinecone]

'normal' should be first/default, to show that's what the text currently is

[essential-randomness]

Spent a bunch of time yesterday exploring this with no success. My hunch is that the implementation of Picker in QuillJS doesn't have a way to mark falsy values (e.g. no value at all, like the normal text in the headers selector) as selected.