> When you say "non-orthogonal", presumably you are suggesting that
> changing one attribute automatically either changes some others
> or restricts some others.  Which such search attributes did you
> have in mind?

I don't know which eli had in mind but:
Word search is non orthogonal to symbol search (I guess they're different values of the same attribute).
Char folding, word/symbol searching, and regexp searching are all non orthogonal due to implementation details.