I am also writing a book editor and have been wrestling almost a year now with `prosemirror-model` and `prosemirror-view` which are close, but not _quite_ what I need for [queryable and collaborative documents.](https://discuss.prosemirror.net/t/queryable-and-collaborative-prosemirror-documents/8977) I feel your pain.
Dervied subdocuments are an antipattern that has landed me in trouble. I think your problems can be solved by having a single document represent your book and then only showing the active chapter via a `nodeView` linked to state. An example is the [folding example](https://prosemirror.net/examples/fold/).
For your ToC you can limit headings to plaintext and use a `
` and 2-way bind the inputs. It should be pretty easy to make a transaction to replace the heading’s text from an `onchange` or `oninput` event. If your heading schema is more complicated you’ll want `
` with a derived schema that contains `nodes: { li: { ...bookSchema.nodes.heading, ...yourImpl } }`. Your 2-way binding will then require remapping transactions from the ToC editor to the book editor. You could even 2-way bind the selection if you really wanted.
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_[View the full topic](https://discuss.prosemirror.net/t/patterns-for-rendering-subsets-of-a-document/9002)._