The default behavior is to match any part of the word, which is useful in some cases, but more often than not I get too many results for some key words that match random unrelated works. Example ai will match to a large fraction of my notes, while as a word I will find only relevant documents. I can use a regular expression like /\Wai\W/ and it does what I need, but it’s a bit inconvenient to do it each time when I search for a specific term. Most search engines perform word matching and I sort of expect it by default.
You probably already know this, but just in case, this is from the online help:
Words in the search query separated by space will be searched independently in each note. For example foo bar will find a note that includes both foo and bar anywhere in it.
"Quoted strings" can be used to search multiple consecutive words separated by space, or in other words, a phrase. So, searching for "foo bar" with quotes will only find notes that include those words next to each other. You can use backslash \" to escape double quotes if you actually want to search for a string that includes quotes. And \\ will do the same for backslash.