This element should appear directly inside a rule element and is used to define conditions for the rule. Within the conditions can be placed content, member and triple elements. For outliners, use the outlinerrow element instead of the content element. These may have attributes whose value is a variable name beginning with a question mark (?). When evaluating the rule for a particular RDF resource, the variables are replaced with values from the resource. If all variables can be replaced, the rule matched.