How about:
Data|Validation|Custom:
formula is:
=OR(A1=0,A1="0",A1=".",
SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(lower( A1),"r",""),"l",""),
"b",""),"w","")="")
all one line

=substitute() is case sensitive. If you really meant rlbw--and not RLBW, then
get rid of that lower() stuff.



Neil wrote:

I would like to validate cells according to the following rule ...

The cell can contain the following:
A single zero "0" or
a single period "." or
a string of any length consisting of the letters R, W, B, L

Eg all the following are valid
0
.
rrr
bbbbb
bbrrl
l
wrbblllrrrrbbbbbb

The following are invalid
00
0r
rrrbbbh
.rbl

Is this possible using a custom validation?

Thanks in advance.
Neil

--

Dave Peterson