+ before a search term means it must be included in the results, so the following produces a boolean
(this also works on quoted phrases, optional ninja options, etc.)
You can test it out here
Why don't we do
AND by default?
Well, we use
OR searches by default and sort by relevance...so effectively you see
AND results before
OR results in the results that come up. Compare the results above to the
OR version you get by default, see how the first results are the same? That's because something with both terms is simply more relevant than anything that has just one. So effectively (at least on the relevance sort),
AND is a subset of
OR, and it'd just be cutting the result list off at whatever the
AND endpoint is...we'd rather give you all the relevant results and stick the stuff that may not be as matchy at the end.