I have selected the option "Everything" (rather than 'All Fields & Tags' or 'Title, Creator, Year') so that I can search through the content of my PDFs. I am trying to find items that contain the exact phrase 'nation'; however, when typing in "nation" (the screen displays 'Advanced search mode -- press Enter to seach.'), Zotero returns many items which don't contain the word at all, but do contain words such as 'national' or 'destination'. How do I search for the exact phrase "nation"?