There seems to be a bug in pldoc that stops parsing when it finds a blank line, this causes the documentation for http_open/3 (for example), to be truncated:
On the web the http_open/3 documentation ends with the option:
raw_encoding(+Encoding)
Do not install a decoding filter for Encoding. For example, using raw_encoding('applocation/gzip') the system will not decompress the stream if it is compressed using gzip.
but if you look at the http_open/3 source code you can see many other options which are not found on the website:
% * raw_headers(-Lines)
% Unify Lines with a list of strings that represents the complete
% reply header returned by the server. See also headers(-List).
%
% * redirect(+Boolean)
% If `false` (default `true`), do _not_ automatically redirect
% if a 3XX code is received. Must be combined with
% status_code(Code) and one of the header options to read the
% redirect reply. In particular, without status_code(Code) a
% redirect is mapped to an exception.
%
% * status_code(-Code)
% If this option is present and Code unifies with the HTTP
% status code, do *not* translate errors (4xx, 5xx) into an
% exception. Instead, http_open/3 behaves as if 2xx (success) is
% returned, providing the application to read the error document
% from the returned stream.
%
% * output(-Out)
% Unify the output stream with Out and do not close it. This can
% be used to upgrade a connection.
%
% * timeout(+Timeout)
% If provided, set a timeout on the stream using set_stream/2.
% With this option if no new data arrives within Timeout seconds
% the stream raises an exception. Default is to wait forever
% (=infinite=).
%
% * post(+Data)
% Issue a =POST= request on the HTTP server. Data is
% handed to http_post_data/3.
%
% * proxy(+Host:Port)
% Use an HTTP proxy to connect to the outside world. See also
% socket:proxy_for_url/3. This option overrules the proxy
% specification defined by socket:proxy_for_url/3.
%
% * proxy(+Host, +Port)
% Synonym for proxy(+Host:Port). Deprecated.
%
% * proxy_authorization(+Authorization)
% Send authorization to the proxy. Otherwise the same as the
% =authorization= option.
%
% * bypass_proxy(+Boolean)
% If =true=, bypass proxy hooks. Default is =false=.
%
% * request_header(Name = Value)
% Additional name-value parts are added in the order of
% appearance to the HTTP request header. No interpretation is
% done.
%
% * max_redirect(+Max)
% Sets the maximum length of a redirection chain. This is needed
% for some IRIs that redirect indefinitely to other IRIs without
% looping (e.g., redirecting to IRIs with a random element in them).
% Max must be either a non-negative integer or the atom `infinite`.
% The default value is `10`.
%
% * user_agent(+Agent)
% Defines the value of the =|User-Agent|= field of the HTTP
% header. Default is =SWI-Prolog=.
%
% The hook http:open_options/2 can be used to provide default
% options based on the broken-down URL. The option
% status_code(-Code) is particularly useful to query *REST*
% interfaces that commonly return status codes other than `200`
% that need to be be processed by the client code.
%
% @param URL is either an atom or string (url) or a list of _parts_.
%
% When provided, this list may contain the fields
% =scheme=, =user=, =password=, =host=, =port=, =path=
% and either =query_string= (whose argument is an atom)
% or =search= (whose argument is a list of
% =|Name(Value)|= or =|Name=Value|= compound terms).
% Only =host= is mandatory. The example below opens the
% URL =|http://www.example.com/my/path?q=Hello%20World&lang=en|=.
% Note that values must *not* be quoted because the
% library inserts the required quotes.
%
% ```
% http_open([ host('www.example.com'),
% path('/my/path'),
% search([ q='Hello world',
% lang=en
% ])
% ])
% ```
%
% @throws error(existence_error(url, Id),Context) is raised if the
% HTTP result code is not in the range 200..299. Context has the
% shape context(Message, status(Code, TextCode)), where `Code` is the
% numeric HTTP code and `TextCode` is the textual description thereof
% provided by the server. `Message` may provide additional details or
% may be unbound.
%
% @see ssl_context/3 for SSL related options if
% library(http/http_ssl_plugin) is loaded.
I spent about 45 minutes looking around the website to find the way to get the http status code back without throwing an exception, but it wasn’t there. I thought to myself, Jan doesn’t code this way 
“I am sure he provided an option to get the http status code back” 
So I went to look at the source code and sure enough, I found it (aptly named status_code(-Code). This is when I saw the blank line above the raw_headers(-Lines) option, surmising that Pldoc had stopped parsing after the blank line.
I think pldoc should be less strict and continue parsing after blank lines, otherwise users of the documentation may never now they are missing a good chunk of the documentation, and it may even take months for developers to see error, so all in all I think it is better to make pldoc more flexible. I happened to find it because I know the kind of developer Jan is, but I don’t think the average prolog user would be able to predict it. They may just spend time coding it when it was there all along.
