Hilite groups with new msgs?

Hello! Is there currently a way to tell slrn to highlight groups that
received new messages after I left them?

IOW, in group display mode, after checking for new articles (with [g])
I'd like to see a character beside each group whose "High water mark"
has changed since the last time I quit that group.

Is something like this already feasible, or would it require hacking the
source code?

TIA,
DN

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