What is the script for selecting a specific word in a field?

[Robert Ball]

I have a field YourAnswer with several instances of xxx. I want to tab 
to each instance of xxx. The scripts

on tabKey
   find word xxx in field "YourAnswer"
end tabKey

and

on tabKey
   find "xxx" in field "YourAnswer"
end tabKey

work, but they give me an outline box around xxx, which is not the same 
thing as selecting xxx, which hilites xxx.

The analogous script

on tabKey
   select word xxx in field "YourAnswer"
end tabKey

does not work. Neither do

on tabKey
   select word xxx of field "YourAnswer"
end tabKey

or

on tabKey
   select "xxx" of field "YourAnswer"
end tabKey


Help!