"exact phrase" matches as a unit. OR between terms (plain terms are AND'd together by default). -term excludes.
from:username restricts to one author. before:YYYY-MM-DD and after:YYYY-MM-DD restrict by date. in:discussions or in:posts restricts to one content type.
Post, discussion, and comment search only looks at the 100 most recent of each, newest first. Electives and people are not affected by these operators.