Intercept scroll in RichEdit/Tmemo

Hi again!

How do I trap scroll of text-area in RichEdit/Memo?
End user should be alowed to try squeeze in a extra
line without scroll of text-area, if it don't fint nothing more
than beep (and of course no linefeed) should happend,
is this possible?
In RichEdit user may use diffent font/font-size so number
of lines won't work!

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