Lee Harris wrote:
Where does one find out in detail about this and
other Excel functions outside Excels own help
for example, I often see formulas such as
=SUMPRODUCT(--(A1:A10=B1:B10),(C1:C10))
[....]
where is that detailed in the help, or on the web?

I am so-o glad you asked this question. I have been
meaning to post a similar question for a long time,
but I keep forgetting.

Someone posted an answer for SUMPRODUCT per se. That
is great. Thanks.

But I would like to know the answer to the more
general question: where to find all such tricks,
which seem to be undocumented? At least, I do not
see them on the standard Help page.

For example, I undertstand the tricks used in the
SUMPRODUCT example above. But I cannot apply the
same trick (an operation on an entire range) in some
other functions, although I believe I have seen the
tricks used by others in some other functions.

Bottom line: how do we know when such tricks will
and will not work? Are there syntactic rules that
govern this? Or are they discovered by trial and
error?

For instance (strawman): Do such tricks work only
with functions that are designed normally to do
element-by-element operations on ranges, for example
as SUMPRODUCT is, but SUM is not?