is a Boolean-valued field. It only accepts the values true and false.
 Example: to find images which are not animated, you would use animated:false.
 is a numerical range field. Four qualifiers, gte (greater than or equal), lte (less than or equal), gt (greater than), and lt (less than), can be applied to the desired value.
 Example: to find images with a score greater than 100, you would use score.gt:100 .
 is a date/time field. It accepts a 
tweaked subset of the ISO 8601 standard, as well as relative dates 
(X minutes/hours/days/months/years ago). Four qualifiers, 
gte (greater than or equal), 
lte (less than or equal), 
gt (greater than), and 
lt (less than), can be applied to the desired value. 
Example: to find images created before 2013, you would use 
created_at.lt:2013 .
 is a literal field. You can apply apply a wildcard  * as a substitute for zero or more characters.
 Example: to find images from DeviantArt, you would use source_url:*deviantart.com* .