The word "Reagan" is not in the title. However, "Reagan's", is. A search for "Reagan's" returns the proper search. And the search feature doesn't work for words with less than 4 letters in them.
So apparently the search engines modus operandi is to split titles into words (splitting on white space), then index words >= 4 characters long. No matching on a substring of such a word. The word
Reagan is in no way related to the word
Reagan's.
Ok - that's an algorithm, as they say. Good as any.
You don't recall seeing this documented anywhere, do you? Or is it up to each of us individually to stumble through the umpteen possible permutations of a search engine, deciphering the behaviour the this one?
... sorry for the rant ... not really fair of me ... thanks for a useful answer.