Top mark in German? (6)

I believe the answer is:

umlaut

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'top mark' is the definition.
'umlaut' can be an answer for 'mark' (umlaut is a kind of mark). I am not sure about the 'top' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for umlaut that I've seen before include "Mark indicating changed vowel value in German" , "Diacritical mark (two dots) placed over a vowel in German to indicate a change in sound" , "Mark over vowel in German to indicate change in pronunciation" , "German accent" , "Dots over letter (indicating vowel change)" .)

I've seen this clue in The Telegraph.

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