Index: docutils/writers/html4css1/__init__.py
===================================================================
--- docutils/writers/html4css1/__init__.py	(revision 5506)
+++ docutils/writers/html4css1/__init__.py	(working copy)
@@ -150,8 +150,20 @@
         writers.Writer.__init__(self)
         self.translator_class = HTMLTranslator
 
+    def set_external_ids(self, extids):
+        """Set a mapping of node IDs to URIs.  Useful for replacing internal
+        references with external ones (it adds support for chunked HTML).
+        The mapping is not used by the writer itself, but the translator
+        object:  If it has a method called ``set_external_ids``, the mapping
+        will be passed to it.
+        """
+        self.external_ids = extids
+
     def translate(self):
         self.visitor = visitor = self.translator_class(self.document)
+        if callable(getattr(visitor, 'set_external_ids', None))\
+           and hasattr(self, 'external_ids'):
+            visitor.set_external_ids(self.external_ids)
         self.document.walkabout(visitor)
         for attr in self.visitor_attributes:
             setattr(self, attr, getattr(visitor, attr))
@@ -298,6 +310,30 @@
         self.in_mailto = 0
         self.author_in_authors = None
 
+        # Mapping of IDs to URIs, set by set_external_ids(), and used by
+        # get_href().
+        self.external_ids = {}
+
+    def set_external_ids(self, extids):
+        """Set a mapping of IDs to URIs.  Useful for replacing internal
+        references with external ones.
+        """
+        self.external_ids = extids
+
+    def get_href(self, id):
+        """Return the node ID as a string suitable for the "href" HTML
+        attribute.  This is usually just ``'#' + id``, but it can also be an
+        URI if the ID is in the mapping set by the ``set_external_ids()``
+        method.  In any case, you don't need to add the '#' character to the
+        string---this method takes care of it.
+
+        *Use this method whenever you need to construct an "href" from an ID.*
+        """
+        try:
+            return self.external_ids[id]
+        except KeyError:
+            return '#' + id
+
     def astext(self):
         return ''.join(self.head_prefix + self.head
                        + self.stylesheet + self.body_prefix
@@ -549,7 +585,7 @@
                          '</tbody>\n</table>\n')
 
     def visit_citation_reference(self, node):
-        href = '#' + node['refid']
+        href = self.get_href(node['refid'])
         self.body.append(self.starttag(
             node, 'a', '[', CLASS='citation-reference', href=href))
 
@@ -879,13 +915,13 @@
             if len(backrefs) == 1:
                 self.context.append('')
                 self.context.append('</a>')
-                self.context.append('<a class="fn-backref" href="#%s">'
-                                    % backrefs[0])
+                self.context.append('<a class="fn-backref" href="%s">'
+                                    % self.get_href(backrefs[0]))
             else:
                 i = 1
                 for backref in backrefs:
-                    backlinks.append('<a class="fn-backref" href="#%s">%s</a>'
-                                     % (backref, i))
+                    backlinks.append('<a class="fn-backref" href="%s">%s</a>'
+                                     % (self.get_href(backref), i))
                     i += 1
                 self.context.append('<em>(%s)</em> ' % ', '.join(backlinks))
                 self.context += ['', '']
@@ -905,7 +941,7 @@
                          '</tbody>\n</table>\n')
 
     def visit_footnote_reference(self, node):
-        href = '#' + node['refid']
+        href = self.get_href(node['refid'])
         format = self.settings.footnote_references
         if format == 'brackets':
             suffix = '['
@@ -1187,7 +1223,7 @@
 
     def visit_problematic(self, node):
         if node.hasattr('refid'):
-            self.body.append('<a href="#%s">' % node['refid'])
+            self.body.append('<a href="%s">' % self.get_href(node['refid']))
             self.context.append('</a>')
         else:
             self.context.append('')
@@ -1220,8 +1256,11 @@
         else:
             assert node.has_key('refid'), \
                    'References must have "refuri" or "refid" attribute.'
-            atts['href'] = '#' + node['refid']
-            atts['class'] += ' internal'
+            atts['href'] = self.get_href(node['refid'])
+            if atts['href'].startswith('#'):
+                atts['class'] += ' internal'
+            else:
+                atts['class'] += ' external'
         if not isinstance(node.parent, nodes.TextElement):
             assert len(node) == 1 and isinstance(node[0], nodes.image)
             atts['class'] += ' image-reference'
@@ -1334,13 +1373,14 @@
         if len(node['backrefs']):
             backrefs = node['backrefs']
             if len(backrefs) == 1:
-                backref_text = ('; <em><a href="#%s">backlink</a></em>'
-                                % backrefs[0])
+                backref_text = ('; <em><a href="%s">backlink</a></em>'
+                                % self.get_href(backrefs[0]))
             else:
                 i = 1
                 backlinks = []
                 for backref in backrefs:
-                    backlinks.append('<a href="#%s">%s</a>' % (backref, i))
+                    backlinks.append('<a href="%s">%s</a>'
+                                     % (self.get_href(backref), i))
                     i += 1
                 backref_text = ('; <em>backlinks: %s</em>'
                                 % ', '.join(backlinks))
@@ -1445,7 +1485,7 @@
             atts = {}
             if node.hasattr('refid'):
                 atts['class'] = 'toc-backref'
-                atts['href'] = '#' + node['refid']
+                atts['href'] = self.get_href(node['refid'])
             if atts:
                 self.body.append(self.starttag({}, 'a', '', **atts))
                 close_tag = '</a></h%s>\n' % (h_level)