Always type these operators capitalized. Finally, you can choose what part of the database to use and how the fields shall be combined. However, bear in mind that too narrow querys may be resultless. A search string will be detected if it is part of any word in the corresponding field in the database. For instance, the search string form in the title field will detect references having for instance the words form , form ula , trans form , and per form ance in their title.
Searches using the abstract field is subject for a warning.
I have not yet added abstracts at all in my database. The search is case insensitive. It is also accent insensitive to some extent.