Sources: GURPS Uplift,
By default, all search terms are optional. It behaves like an OR logic. Objects that contain the more terms are rated higher in the results and will appear first in their type. For example, wiki forum will find:
Add a plus sign ( + ) before a term to indicate that the term must appear in results. Example: +wiki forum will find objects containing at least wiki. Objects with both terms and many occurences of the terms will appear first.
Add a minus sign ( - ) before a term to indicate that the term must not appear in the results. To reduce a term's value without completely excluding it, use a tilde. Example: -wiki forum will find objects that do not contain wiki but contain forum
Use parenthesis ( ) to group terms into subexpressions. Example: +wiki +(forum blog) will find objects that contain wiki and forum or that contain wiki and blog in any order.
Use double quotes ( " " ) around a phrase to find terms in the exact order, exactly as typed. Example: "Alex Bell" will not find Bell Alex or Alex G. Bell.
Add an asterisk ( * ) after a term to find objects that include the root word. For example, run* will find:
Add a tilde ( ~ ) before a term to reduce its value indicate to the ranking of the results. Objects that contain the term will appear lower than other objects (unlike the minus sign which will completely exclude a term). Example: +wiki ~forum will rate an object with only wiki higher that an object with wiki and forum.
Add a less than ( < ) or greater than ( > ) sign before a term to change the term's contribution to the overall relevance value assigned to a object. Example: +wiki +(>forum < blog) will find objects that contain wiki and forum or wiki and blog in any order. wiki forum will be rated higher.