- Patch #1482 by djun: we're moving the DocBook output to a contributed module.  It's not a core feature.

  The book module's current administration is actually a patchwork of one form per book page crammed into a table with another form at the bottom. This simply didn't work.

- Patch #38296 by Ber: generate rel-tags for book pages.  Makes it easier to browse in some browsers.

  TODO:
  + The contact.module was broken; a new patch for contact.module is needed.
  + Documentation is needed.
  + The most important modules need to be updated ASAP.

  input validation error..

All node revisions were stored in a serialized field in the node table and retrieved for _each_ page view although they are rarely needed. We created a separate revisions table which would be in principle identical to the node table, only that it could have several old copies of the same node.  This also allows us to revision-related information, and to provide log entries to non-book pages when a new revision is being created.

TODO:

1. Provide upgrade instructions for node module maintainers!
2. Upgrade modules that implement node types.
3. Provide an upgarde path for revisions.  Dependency on the upgrade system.

  part of the node system!  If you have a module that implements node
  types, you'll have to udpate its CVS HEAD version.

  We replaced _node_name() and _node_types() by _node().  The new _node()
  hook let's you define one or more node types, including their names.
  The implementation of the _node() hook needs to:

   return array($type1 => array('name' => $name1, 'base' => $base1),
                $type2 => array('name' => $name2, 'base' => $base2));

  where $type is the node type, $name is the human readable name of the type
  and $base is used instead of <hook> for <hook>_load, <hook>_view, etc.

  For example, the story module's node hook looks like this:

    function story_node() {
      return array('story' => array('name' => t('story'), 'base' => 'story'));
    }

  The page module's node hook module like:

    function page_node() {
      return array('page' => array('name' => t('page'), 'base' => 'page'));
    }

  However, more complex node modules like the project module and the
  flexinode module can use the 'base' parameter to specify a different base.

  The project module implements two node types, proejcts and issues, so it
  can do:

    function project_node() {
      return array(
       array('project_project' => array('name' => t('project'), 'base' => 'project'),
       array('project_issue' => array('name' => t('issue'), 'base' => 'project_issue'));
    }

  In the flexinode module's case there can only one base ...

  This hook will simplify the CCK, and will make it easy (or easier) to merge
  the story and page module.

  In addition, node_list() became node_get_types().  In addition, we created
  the following functions: node_get_name($type) and node_get_base($type).

  TODO: document the defaults in the PHPdoc comments.

  to OPML export functionality, better code comments, better help texts, etc.

See:
http://cvs.drupal.org/viewcvs/drupal/drupal/modules/book.module?r1=1.294&r2=1.295

This patch enables export of books as XML documents.

The XML is DocBook "at the level of structure", but
node contents are wrapped as CDATA, since we
can't be sure that the contents are valid XML.

Several other bugs/feature requests are also
addressed with this patch:

- Fixes bugs

http://drupal.org/node/1898
http://drupal.org/node/1482
http://drupal.org/node/8049
http://drupal.org/node/1899

Should go a long way towards implementing feature request
http://drupal.org/node/2062

It should also be easy to extend this to produce OPML,
for example.

- Adds about 170 lines, of which more than 100 are comments
- Added doxygen comments
- Made doxygen comment format consistent; fixed minor grammatical slips
- A proper Doctype and more informative HTML element is generated
for printer-friendly HTML output.
- Refactored book_print() to use book_recurse().
- Refactored book_recurse(). Applies 'visitor' callback functions to nodes
during weight/title order tree-traversal. The parameterized
visitor callbacks can be used to generate different kinds of output.
There are many other kinds of operations on books which can be implemented
by writing a pre-node/post-node pair of callback functions: word-count/
statistics gathering, comparison, copying, search and replace...
- Introduced book_export() which uses book_recurse() to generate
DocBook-like XML to export book contents in a structured form.
An md5 hash is computed for each node to help import code to
decide if a node needs to be updated or not.

  TODO: we should write down a couple guidelines for these document them in
        the PHPDoc code of drupal_set_message()!  .