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+nghttp2 Documentation
+=====================
+
+The documentation of nghttp2 is generated using Sphinx.  This
+directory contains the source files to be processed by Sphinx.  The
+source file for API reference is generated using a script called
+``mkapiref.py`` from the nghttp2 C source code.
+
+Generating API reference
+------------------------
+
+As described earlier, we use ``mkapiref.py`` to generate rst formatted
+text of API reference from C source code.  The ``mkapiref.py`` is not
+so flexible and it requires that C source code is formatted in rather
+strict rules.
+
+To generate API reference, just run ``make html``. It runs
+``mkapiref.py`` and then run Sphinx to build the entire document.
+
+The ``mkapiref.py`` reads C source code and searches the comment block
+starts with ``/**``. In other words, it only processes the comment
+block starting ``/**``. The comment block must end with ``*/``. The
+``mkapiref.py`` requires that which type of the object this comment
+block refers to.  To specify the type of the object, the next line
+must contain the so-called action keyword.  Currently, the following
+action keywords are supported: ``@function``, ``@functypedef``,
+``@enum``, ``@struct`` and ``@union``. The following sections
+describes each action keyword.
+
+@function
+#########
+
+``@function`` is used to refer to the function.  The comment block is
+used for the document for the function.  After the script sees the end
+of the comment block, it consumes the lines as the function
+declaration until the line which ends with ``;`` is encountered.
+
+In Sphinx doc, usually the function argument is formatted like
+``*this*``.  But in C, ``*`` is used for dereferencing a pointer and
+we must escape ``*`` with a back slash. To avoid this, we format the
+argument like ``|this|``. The ``mkapiref.py`` translates it with
+``*this*``, as escaping ``*`` inside ``|`` and ``|`` as necessary.
+Note that this shadows the substitution feature of Sphinx.
+
+The example follows::
+
+    /**
+     * @function
+     *
+     * Submits PING frame to the |session|.
+     */
+    int nghttp2_submit_ping(nghttp2_session *session);
+
+
+@functypedef
+############
+
+``@functypedef`` is used to refer to the typedef of the function
+pointer. The formatting rule is pretty much the same with
+``@function``, but this outputs ``type`` domain, rather than
+``function`` domain.
+
+The example follows::
+
+    /**
+     * @functypedef
+     *
+     * Callback function invoked when |session| wants to send data to
+     * remote peer.
+     */
+    typedef ssize_t (*nghttp2_send_callback)
+    (nghttp2_session *session,
+     const uint8_t *data, size_t length, int flags, void *user_data);
+
+@enum
+#####
+
+``@enum`` is used to refer to the enum.  Currently, only enum typedefs
+are supported.  The comment block is used for the document for the
+enum type itself. To document each values, put comment block starting
+with the line ``/**`` and ending with the ``*/`` just before the enum
+value.  When the line starts with ``}`` is encountered, the
+``mkapiref.py`` extracts strings next to ``}`` as the name of enum.
+
+At the time of this writing, Sphinx does not support enum type. So we
+use ``type`` domain for enum it self and ``macro`` domain for each
+value. To refer to the enum value, use ``:enum:`` pseudo role. The
+``mkapiref.py`` replaces it with ``:macro:``. By doing this, when
+Sphinx will support enum officially, we can replace ``:enum:`` with
+the official role easily.
+
+The example follows::
+
+    /**
+     * @enum
+     * Error codes used in the nghttp2 library.
+     */
+    typedef enum {
+      /**
+       * Invalid argument passed.
+       */
+      NGHTTP2_ERR_INVALID_ARGUMENT = -501,
+      /**
+       * Zlib error.
+       */
+      NGHTTP2_ERR_ZLIB = -502,
+    } nghttp2_error;
+
+@struct
+#######
+
+``@struct`` is used to refer to the struct. Currently, only struct
+typedefs are supported. The comment block is used for the document for
+the struct type itself.To document each member, put comment block
+starting with the line ``/**`` and ending with the ``*/`` just before
+the member.  When the line starts with ``}`` is encountered, the
+``mkapiref.py`` extracts strings next to ``}`` as the name of struct.
+The block-less typedef is also supported. In this case, typedef
+declaration must be all in one line and the ``mkapiref.py`` uses last
+word as the name of struct.
+
+Some examples follow::
+    
+    /**
+     * @struct
+     * The control frame header.
+     */
+    typedef struct {
+      /**
+       * SPDY protocol version.
+       */
+      uint16_t version;
+      /**
+       * The type of this control frame.
+       */
+      uint16_t type;
+      /**
+       * The control frame flags.
+       */
+      uint8_t flags;
+      /**
+       * The length field of this control frame.
+       */
+      int32_t length;
+    } nghttp2_ctrl_hd;
+        
+    /**
+     * @struct
+     *
+     * The primary structure to hold the resources needed for a SPDY
+     * session. The details of this structure is hidden from the public
+     * API.
+     */
+    typedef struct nghttp2_session nghttp2_session;
+
+@union
+######
+
+``@union`` is used to refer to the union. Currently, ``@union`` is an
+alias of ``@struct``.