keywords [keywords] will search for keywords only
lower [username] will search for submissions posted by a specific user
title [title] will search for a title
message [search terms] will search in the description
filename [search terms] will search for the terms in the submission filename (not really useful imho but it's nice to have nonetheless)
| means 'OR' (not an absolute OR though so it can match various patterns)
& means 'AND' (useful to exclude a set of things or make sure two or more patterns are both present)
! means 'NOT' it negates the pattern following it. It can also be used for keywords so for example fox !wolf.