convert blank lines to <br>

cms/static/grammar.jspeg

 start
-  = sections:(StringResponse / NumericalResponse / MultipleChoice / Paragraph / Linebreak+)+
-    {
-      var hasKind = function(o) {
-        return o.hasOwnProperty('type');
-      }
-      return sections.filter(hasKind);
-    }
+  = sections:(StringResponse / NumericalResponse / MultipleChoice / Paragraph / PreservedLinebreaks)+
 
 StudentProducedResponseIdentifier
   = '='
@@ -76,7 +70,7 @@ Paragraph
 Line
   = text:Text terminator:Linebreak
     {
-      return text + terminator;
+      return text + '\n';
     }
 
 Text
@@ -88,6 +82,12 @@ Text
 OptionalSpaces
   = ' '*
 
+PreservedLinebreaks
+  = terminators:('\n')+
+  {
+    return {'type': 'linebreaks', 'count': terminators.length}
+  }
+
 Linebreak
   = ('\n')
 

common/lib/xmodule/xmodule/js/src/capa/edit.coffee

@@ -24,6 +24,7 @@ class @CapaDescriptor
         try
             source = @source_box.val() + "\n"
             result = @parser.parse (source)
+            console.log result
             @outputXML(result)
             @message_box.css {"display":"none"}
         catch e 
@@ -37,7 +38,8 @@ class @CapaDescriptor
     dom2capa: (node) ->
         capa = new XMLSerializer().serializeToString(node)
         capa = capa + ""
-        return capa.replace(/<startouttext>/g, '<startouttext />').replace(/<\/startouttext>/g, '<endouttext />')
+        return capa.replace(/<startouttext>/g, '<startouttext />')
+                   .replace(/<\/startouttext>/g, '<endouttext />')
 
     buildXML: (parsed) ->
         dom_parser = new DOMParser()
@@ -54,6 +56,13 @@ class @CapaDescriptor
                 newel = create_text_element(section.text)
                 problem.append(newel)
 
+            else if section.type == 'linebreaks'
+                text = create_text_element('')
+                for i in [0..section.count] by 1
+                    br = doc.createElement('br')
+                    text.append(br)
+                problem.append(text)
+
             else if section.type == 'multiple_choice'
                 newel = $(doc.createElement('choiceresponse'))