I run Excel 2003.
I composed a cell with the value 4.6@3
Excel chose to give that text a color of blue, underline it and
interpret it as a mailto, so that clicking on it causes my email program
to open. I do not want that special action.
I changed color to automatic and removed the underline, but the cell is
still interpreted as a mailto. I know that prefixing a number with a
prime character, causes it to be interpreted as text - where is that
documented? - but '4.6@3 is also interpreted as a mailto.

How do I stop 4.6@3 being interpreted as a mailto?
A reference to a help topic would be best, but I will gladly accept a
heuristic.

I have answered my own question.
The relevant help topic is "Remove a hyperlink" where "Deactivate a
single hyperlink" says "Right-click the hyperlink you want to
deactivate, and then click Remove Hyperlink on the shortcut menu."

I have a supplementary question. How do I stop Excel interpreting cells
as hyperlinks? I found nothing obvious in Tools\Options.

I will repeat the question already asked in passing, above.
Where is the use of prime (') to cause a number to be interpreted as
text documented?

I think there is a general question there. How do I control special
action by Excel on entering a set of characters into a cell?
--
Walter Briscoe