All headers are optional and the default value is not to use any of these headers at all. All headers are optional but the default behavior is to use all request headers except From and Pragma . The reason is that the former in general requires permission by the user and the latter has special meanings for proxy servers. The entity headers contain information about the object sent in the HTTP transaction. This flag defines which headers are to be sent in a request together with an entity body.
All headers are optional but the default value is to use as many as possible.
When a header is parsed, the information is first stored in an HTResponse object. The set of headers directly handled by the internal MIME parser is the reader is referred to the actual implementation in order to see the exact list. In many cases, if you have registered an extra set of headers to be generated, you are also in a situation where you would like to handle the result that is returned by the remote server. As we will describe in this section, the Library provides a very similar interface to the one presented above for generating extra headers. In case a parser is found for this particular header, the call back is called with the header and all parameters that might follow it.