Why can't you? Assuming your Field Codes are showing, you can select
any or all the characters inside the braces -- you can even select
part outside, part inside the braces (though you probably shouldn't).
Maybe you have "Smart selection" turned on? (Which seems to think you
wouldn't want ever to select anything less than a whole word.)
Or are you talking about selecting some text in an Index that's
already been generated? IIRC you can do that not by clicking inside
the Index (which is itself a giant Field) but by sneaking up on it
using the arrow keys.
