Currently, indication, that any mentions have successfully occurred, is provided to the editor only by an opt-in notification implemented in {T139623}. Although useful, this solution has [[ #3260175 | severe usability issues ]].
The request is to enhance the **edit preview** and **"Your edit was saved" message** to indicate the mentions there.
This will not be trivial, because notification processing is deferred for later to achieve fast save response and we do not want to change that. Therefore the mentions are not yet available at the time of responding to the save request.
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Suggestion below, is to indicate "N editors were mentioned", (rather than implying that they have actually been notified, which they might not depending on their userpreferences).
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See also: {T78424}