Citrix Systems Network Router 9.2 User Manual

Advanced policies evaluate data on the basis of information that you supply in 
advanced expressions. An advanced expression analyzes data elements (for 
example, HTTP headers, source IP addresses, the NetScaler system time, and 
POST body data). 

To create an advanced expression, you select a prefix that identifies a piece of 
data that you want to analyze, and then you specify an operation to perform on the 
data. For example, an operation can match a piece of data with a text string that 
you specify, or it can transform a text string into an HTTP header. Other 
operations match a returned string with a set of strings or a string pattern. You 
configure compound expressions by specifying Boolean and arithmetic operators, 
and by using parentheses to control the order of evaluation. You can also include 
classic expressions in an advanced expression.

Advanced expressions are typically part of a policy, and you can assign names to 
frequently used expressions so that you do not have to enter the full expression 
repeatedly in multiple policies. But for some features, you configure advanced 
expressions outside the context of a policy.