Most properties in a request object contain information about the request that comes from the HTTP request header. Not every request supplies a value for every one of these properties. Also, some requests may include header fields that are not surfaced in a property of the request object, especially as the HTTP standard continues to evolve. To obtain the value of a request header field that is not surfaced as one of the properties of the request object, use the GetFieldByName method. 

The request header properties can be categorized by function:

• Properties that identify the target
• Properties that describe the Web client
• Properties that identify the purpose of the request
• Properties that describe the expected response
• Properties that describe the content