The (basically excellent now that I know it's there) searching cheat sheet on the Quick Search settings page explains the default Boolean backwards.
The default (space equals) Boolean is AND (thank god!), but the help portrays it as if it was OR. The example is "[keywords] this that theother" with text that says "the keywords field must contain one of this, that, or theother"
The next line has in the example "this and that and theother". The text says that the field "must contain all of this, that, and theother". Which is correct, whether or not the Booleans have been typed in.
By the way, thank you for allowing lower case Booleans. Some systems make you type them in all caps, which is a pain in the neck. For the benefit of lurkers: I type Booleans all caps in conversation for the sake of clarity, but that is/should be unnecessary in search because they're all stop words. (Words not searched by the system because they're too common.)
