simple function to prepend a string to a file

[ken]

Often I want to put the string "<!-- -*- coding: utf-8; -*- -->\n" at
the top of the current buffer.  However, I don't want to lose my place
(the point) or any defined region.  Optimally, such a function would
know the mode of the current buffer and enclose the string in the
mode-appropriate comment characters.  Is there such a function?  If not
how would one code it?

Thanks for your solutions.

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first create the universe."
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