On my website I have a search bar. It's powered by Lucene.net. I have a requirement to make search be a substring case insensitive search, with direct hits appearing before substrings. What I don't know, however, is when a user searches for a multi-word item--say "Chocolate Milk"--should that be treated under the hood as an AND or OR search?
As an example:
*chocolate* AND *milk*
*chocolate* OR *milk*
The requirement right now is to treat this as an AND, but I'm not sure if that's the right way to go about it. What would be the best in terms of UX?
I would think the best thing to do would be an OR search, with items containing both keywords appearing before items containing only one of the keywords. Thoughts?
EDIT: The types of items being searched are medical supplies, with very cryptic names.