Providing "descriptions" for VBA User Function Arguments

I posted this query on the Miscellaneous forum some days ago, and got a description of how to attach a description to a function.
This was not what I was after. Perhaps someone in this forum can help.

When I click the fx toolbar button with a standard function,
for example ROUND(C11,1) I get the Function Arguments dialog box
with the auguments given as:
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Number C11 = 1405.36
Num_digits 1 = 1

= 1405.4

Rounds a number to a specific number of digits.

Number is the number you want to round.
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The string "Rounds a number to a specific number of digits." is the function description;
but how do I get my function to provide the equivalent of the "is the number you want to round." string?
All I get is (the equivalent of) Number with no followup text.

This would be clearer if I could upload bit-maps to show what I mean, but unfortunately the web security software here precludes this.
I hope my description makes sense to someone out there.

Mark.