When the extend attribute was added to the wikitext (project page), there were no changes for VE implemented (mockup).
Updated requirements can be found in the epic T245299: Sub-reference support in VE. See also T151308: Make VisualEditor compatible with "extends" parameter.
Issues in workflow steps
| Workflow step | Status Quo | Possible improvements |
| Create and edit a reference | References and sub-references are displayed in their own edit dialog   | Add info about related references in edit dialog. Add info on sub-references in parent reference |
| Preview and reflist in VE | Sub-reference is displayed as an independent reference {F36957464} | Display sub-reference in relation to parent (similar to frontend) in VE:  |
| Popup dialog that displays the reference in VE | Sub-reference is only displaying the extend part and not the parent reference  | Display full reference in popup dialog in VE. Mock:  |
| Re-use a reference | Sub-references are displayed as independent references  | Display sub-reference in relation to parent in re-use dialog. |
| Deleting a reference | No warning or prevention to delete parent references in VE  | Display warning when deleting a parent |
See also working document.