Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields using product tokens also allow sub-products which form a significant part of the application to be listed, separated by whitespace. By convention, the products are listed in order of their significance for identifying the application.
product = token ["/" product-version] product-version = token
User-Agent: CERN-LineMode/2.15 libwww/2.17b3 Server: Apache/0.8.4
Product tokens should be short and to the point -- use of them for advertising or other non-essential information is explicitly forbidden. Although any token character may appear in a product- version, this token SHOULD only be used for a version identifier (i.e., successive versions of the same product SHOULD only differ in the product-version portion of the product value).