Getting linearity to reveal fragments. This avoid rendering of - (none) cells before fragments.

IPython/nbconvert/preprocessors/revealhelp.py

@@ -55,7 +55,14 b' class RevealHelpPreprocessor(Preprocessor):'
                     worksheet.cells[index - 1].metadata.slide_helper = 'slide_end'
                 if cell.metadata.slide_type in ['subslide']:
                     worksheet.cells[index - 1].metadata.slide_helper = 'subslide_end'
-
+                if cell.metadata.slide_type in ['fragment']:
+                    try:
+                        i = 1
+                        while 1:
+                            worksheet.cells[index + i].metadata.frag_helper = 'fragment_end'
+                            i += 1
+                    except IndexError as e:
+                        pass #Last cell doesn't have a next one
 
         if not isinstance(resources['reveal'], dict):
             resources['reveal'] = {}

IPython/nbconvert/templates/html/slides_reveal.tpl

@@ -10,7 +10,13 b''
     <section>
     {{ super() }}
 {%- elif cell.metadata.slide_type in ['-'] -%}
-    {{ super() }}
+    {%- if cell.metadata.frag_helper in ['fragment_end'] -%}
+        <div class="fragment">
+        {{ super() }}
+        </div>
+    {%- else -%}
+        {{ super() }}
+    {%- endif -%}
 {%- elif cell.metadata.slide_type in ['skip'] -%}
     <div style=display:none>
     {{ super() }}