Q: Are Notus documents compatible with Quill documents?
Short answer is no. Even though Notus uses Quill Delta as underlying representation for its documents there are at least differences in attribute declarations. For instance heading style in Quill editor uses "header" as the attribute key, in Notus it's "heading".
There are also semantic differences. In Quill, both list and heading styles are treated as block styles. This means applying "heading" style to a list item removes the item from the list. In Notus, heading style is handled separately from block styles like lists and quotes. As a consequence you can have a heading line inside of a quote block. This is intentional and inspired by how Markdown handles such scenarios. In fact, Notus format tries to follow Markdown semantics as close as possible.