diff --git a/IPython/nbconvert/postprocessors/serve.py b/IPython/nbconvert/postprocessors/serve.py
index 5051454..d2383be 100644
--- a/IPython/nbconvert/postprocessors/serve.py
+++ b/IPython/nbconvert/postprocessors/serve.py
@@ -53,7 +53,7 @@ class ServePostProcessor(PostProcessorBase):
     open_in_browser = Bool(True, config=True,
         help="""Should the browser be opened automatically?"""
     )
-    reveal_cdn = Unicode("https://cdn.jsdelivr.net/reveal.js/2.5.0", config=True,
+    reveal_cdn = Unicode("https://cdn.jsdelivr.net/reveal.js/2.6.2", config=True,
         help="""URL for reveal.js CDN."""
     )
     reveal_prefix = Unicode("reveal.js", config=True, help="URL prefix for reveal.js")
diff --git a/IPython/nbconvert/preprocessors/revealhelp.py b/IPython/nbconvert/preprocessors/revealhelp.py
index 2b910ae..151a223 100755
--- a/IPython/nbconvert/preprocessors/revealhelp.py
+++ b/IPython/nbconvert/preprocessors/revealhelp.py
@@ -56,10 +56,13 @@ class RevealHelpPreprocessor(Preprocessor):
                 if cell.metadata.slide_type in ['subslide']:
                     worksheet.cells[index - 1].metadata.slide_helper = 'subslide_end'
                 #Prevent the rendering of "do nothing" cells before fragments
+                #Group fragments passing frag_number to the data-fragment-index
                 if cell.metadata.slide_type in ['fragment']:
+                    worksheet.cells[index].metadata.frag_number = index
                     i = 1
                     while i < len(worksheet.cells) - index:
                         worksheet.cells[index + i].metadata.frag_helper = 'fragment_end'
+                        worksheet.cells[index + i].metadata.frag_number = index
                         i += 1
                 #Restart the slide_helper when the cell status is changed
                 #to "do nothing".
diff --git a/IPython/nbconvert/templates/html/slides_reveal.tpl b/IPython/nbconvert/templates/html/slides_reveal.tpl
index 2cb112c..e2444f5 100644
--- a/IPython/nbconvert/templates/html/slides_reveal.tpl
+++ b/IPython/nbconvert/templates/html/slides_reveal.tpl
@@ -11,7 +11,7 @@
     {{ super() }}
 {%- elif cell.metadata.slide_type in ['-'] -%}
     {%- if cell.metadata.frag_helper in ['fragment_end'] -%}
-        <div class="fragment">
+        <div class="fragment" data-fragment-index="{{ cell.metadata.frag_number }}">
         {{ super() }}
         </div>
     {%- else -%}
@@ -26,7 +26,7 @@
     {{ super() }}
     </aside>
 {%- elif cell.metadata.slide_type in ['fragment'] -%}
-    <div class="fragment">
+    <div class="fragment" data-fragment-index="{{ cell.metadata.frag_number }}">
     {{ super() }}
     </div>
 {%- endif -%}