T100645 proposes a way to make it easier for readers and editors to understand the sources used in articles by creating a way to refer to different pages of the same work when adding references to an article.
The implementation of the above will affect the experience of contributors editing using the VisualEditor.
This task is about defining what the experience for contributors editing in VE will need to be before the first version of the new sub-referencing feature is deployed. 
- An article's sub-references should appear to you, someone in editing in VE, the same way they appear to you when you are viewing that article's sub-references in read mode.
- As someone editing a sub-reference in VE, it should be clear you are editing a reference that has a relationship to other reference(s)
- As someone editing a sub-reference in VE, it should be clear to you what reference said sub-reference relates to.
- As someone editing a sub-reference in VE, you should not be able to accidentally "orphan" sub-references by deleting their parent reference
- As someone editing in VE, you should not be able to mistakenly break/delete parent references by attempting to edit the contents of a sub-reference or change their group
- The "Requirements" section above is finalized. See: T245299#5939925
- WMF's Editing-team has reached an agreement with the team at WMDE responsible for implementing T100645 that the requirements listed in the "Requirements" section above will be met before any version of the new feature is released
- de.wiki community wishlist discussion: https://de.wikipedia.org/wiki/Wikipedia:Umfragen/Technische_W%C3%BCnsche/Top_20
- Phabricator workboard: https://phabricator.wikimedia.org/tag/book-referencing/
- Prototype: https://de.wikipedia.beta.wmflabs.org/wiki/Faultier
- This project is somewhat unique in so far it introduces new functionality by way of new wikitext syntax which cannot be "rolled back" thus the need for the above "Requirements" to be met before anything is deployed.