Meaning of square brackets in a Preview search I recently needed to search for a string enclosed in square brackets in a PDF document. So I typed [concept] into the search field (including the square brackets).

The result surprised me, as I got a list of pages containing the word concept with all letters contained in that word highlighted in yellow. 

I haven't been able to find any documentation of this "feature" - or any other special syntax in the search field.

What is the straight explanation for this behaviour, if any?
Sounds like the search is actually a Regular Expression search, and by enclosing your search term in brackets, instead of searching for the word 'concept' you were searching for the presence of the letters 'c', 'o', 'n', 'e', 'p' and 't'.