fast_value Syntax Rules
The **fast_value** modifier can be used to modify numeric or length detection fields. The method of using this rule is similar to that of **fast_pattern**. Example: ``` flow: to_server; http_host_len:> 1024; fast_value; http_content_length:>2048; ``` In this signature, **http_host_len** is modified by the **fast_value** keyword. In the pre-filtering, this item is used as a pre-detection item. If the length of the Host field in the traffic is greater than 1024 bytes, the subsequent detection items can be used for matching. The signature writer can use **fast_value** to modify the detection items with obvious threat characteristics to achieve better matching and performance effect.