We need to clarify the meaning of each operator - for example why it's called "SHOULD" rather than OR, and make a clear usage example of the NOT operator.

Also clearly differentiate between a "MUST and a "MUST NOT".

See also:

• https://bugzilla.redhat.com/show_bug.cgi?id=1242701
• http://docs.jboss.org/hibernate/search/5.5/reference/en-US/html_single/#search-query-querydsl
• https://access.redhat.com/documentation/en-US/JBoss_Enterprise_Application_Platform/6.4/html-single/Development_Guide/index.html