The Table of Contents (ToC) vanishes in edit-mode.
Seeing the complete ToC during editing, can help prevent mistakes in both content and article-layout.
This can be particularly problematic in articles that have long infoboxes or many images near the top. We're /meant/ to space items, so that having the ToC collapsed/hidden doesn't negatively effect the layout, but this is often not the case in pages at less than Featured quality.
Version: unspecified
Severity: enhancement
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=53217