diff --git a/blockly_compressed.js b/blockly_compressed.js
index 8c039df0e..d5dfcd985 100644
--- a/blockly_compressed.js
+++ b/blockly_compressed.js
@@ -1320,8 +1320,8 @@ Blockly.WidgetDiv={};Blockly.WidgetDiv.DIV=null;Blockly.WidgetDiv.owner_=null;Bl
 Blockly.WidgetDiv.hide=function(){Blockly.WidgetDiv.owner_&&(Blockly.WidgetDiv.DIV.style.display="none",Blockly.WidgetDiv.dispose_&&Blockly.WidgetDiv.dispose_(),Blockly.WidgetDiv.owner_=null,Blockly.WidgetDiv.dispose_=null,goog.dom.removeChildren(Blockly.WidgetDiv.DIV))};Blockly.WidgetDiv.isVisible=function(){return!!Blockly.WidgetDiv.owner_};Blockly.WidgetDiv.hideIfOwner=function(a){Blockly.WidgetDiv.owner_==a&&Blockly.WidgetDiv.hide()};
 Blockly.WidgetDiv.position=function(a,b,c,d,e){b<d.y&&(b=d.y);e?a>c.width+d.x&&(a=c.width+d.x):a<d.x&&(a=d.x);Blockly.WidgetDiv.DIV.style.left=a+"px";Blockly.WidgetDiv.DIV.style.top=b+"px"};
 // Copyright 2011 Google Inc.  Apache License 2.0
-Blockly.inject=function(a,b){if(!goog.dom.contains(document,a))throw"Error: container is not in current document.";var c=Blockly.parseOptions_(b||{}),d,e=function(){var b=Blockly.createDom_(a,c);d=Blockly.createMainWorkspace_(b,c);Blockly.init_(d);d.markFocused();Blockly.bindEvent_(b,"focus",d,d.markFocused)};if(c.enableRealtime){var f=document.getElementById("realtime");f&&(f.style.display="block");Blockly.Realtime.startRealtime(e,a,c.realtimeOptions)}else e();return d};
-Blockly.parseToolboxTree_=function(a){a?("string"!=typeof a&&"undefined"==typeof XSLTProcessor&&(a=a.outerHTML),"string"==typeof a&&(a=Blockly.Xml.textToDom(a))):a=null;return a};
+Blockly.inject=function(a,b){goog.isString(a)&&(a=document.getElementById(a));if(!goog.dom.contains(document,a))throw"Error: container is not in current document.";var c=Blockly.parseOptions_(b||{}),d,e=function(){goog.dom.removeChildren(a);var b=Blockly.createDom_(a,c);d=Blockly.createMainWorkspace_(b,c);Blockly.init_(d);d.markFocused();Blockly.bindEvent_(b,"focus",d,d.markFocused)};if(c.enableRealtime){var f=document.getElementById("realtime");f&&(f.style.display="block");Blockly.Realtime.startRealtime(e,
+a,c.realtimeOptions)}else e();return d};Blockly.parseToolboxTree_=function(a){a?("string"!=typeof a&&"undefined"==typeof XSLTProcessor&&(a=a.outerHTML),"string"==typeof a&&(a=Blockly.Xml.textToDom(a))):a=null;return a};
 Blockly.parseOptions_=function(a){var b=!!a.readOnly;if(b)var c=null,d=!1,e=!1,f=!1,g=!1,h=!1,k=!1;else c=Blockly.parseToolboxTree_(a.toolbox),d=Boolean(c&&c.getElementsByTagName("category").length),e=a.trashcan,void 0===e&&(e=d),f=a.collapse,void 0===f&&(f=d),g=a.comments,void 0===g&&(g=d),h=a.disable,void 0===h&&(h=d),k=a.sounds,void 0===k&&(k=!0);var l=a.scrollbars;void 0===l&&(l=d);var p=a.css;void 0===p&&(p=!0);var m=a.grid||{};m.spacing=m.spacing?parseFloat(m.spacing):0;m.colour||(m.colour=
 "#888");m.length=m.length?parseFloat(m.length):1;m.snap=!!m.snap;var q="https://blockly-demo.appspot.com/static/media/";a.media?q=a.media:a.path&&(q=a.path+"media/");var n=!!a.realtime;return{RTL:!!a.rtl,collapse:f,comments:g,disable:h,readOnly:b,maxBlocks:a.maxBlocks||Infinity,pathToMedia:q,hasCategories:d,hasScrollbars:l,hasTrashcan:e,hasSounds:k,hasCss:p,languageTree:c,gridOptions:m,enableRealtime:n,realtimeOptions:n?a.realtimeOptions:void 0}};
 Blockly.createDom_=function(a,b){a.setAttribute("dir","LTR");goog.ui.Component.setDefaultRightToLeft(b.RTL);Blockly.Css.inject(b.hasCss,b.pathToMedia);var c=Blockly.createSvgElement("svg",{xmlns:"http://www.w3.org/2000/svg","xmlns:html":"http://www.w3.org/1999/xhtml","xmlns:xlink":"http://www.w3.org/1999/xlink",version:"1.1","class":"blocklySvg"},a),d=Blockly.createSvgElement("defs",{},c),e,f;e=Blockly.createSvgElement("filter",{id:"blocklyEmboss"},d);Blockly.createSvgElement("feGaussianBlur",{"in":"SourceAlpha",
diff --git a/core/inject.js b/core/inject.js
index 42863775d..d134db983 100644
--- a/core/inject.js
+++ b/core/inject.js
@@ -34,12 +34,15 @@ goog.require('goog.userAgent');
 
 
 /**
- * Inject a Blockly editor into the specified container DIV.
- * @param {!Element} container Containing element.
+ * Inject a Blockly editor into the specified container element (usually a div).
+ * @param {!Element|string} container Containing element or its ID.
  * @param {Object} opt_options Optional dictionary of options.
  * @return {!Blockly.Workspace} Newly created main workspace.
  */
 Blockly.inject = function(container, opt_options) {
+  if (goog.isString(container)) {
+    container = document.getElementById(container);
+  }
   // Verify that the container is in document.
   if (!goog.dom.contains(document, container)) {
     throw 'Error: container is not in current document.';
@@ -47,6 +50,7 @@ Blockly.inject = function(container, opt_options) {
   var options = Blockly.parseOptions_(opt_options || {});
   var workspace;
   var startUi = function() {
+    goog.dom.removeChildren(container);
     var svg = Blockly.createDom_(container, options);
     workspace = Blockly.createMainWorkspace_(svg, options);
     Blockly.init_(workspace);
diff --git a/demos/blockfactory/factory.js b/demos/blockfactory/factory.js
index 648fd9616..ecae1e816 100644
--- a/demos/blockfactory/factory.js
+++ b/demos/blockfactory/factory.js
@@ -396,10 +396,8 @@ var oldDir = null;
 function updatePreview() {
   var newDir = document.getElementById('direction').value;
   if (oldDir != newDir) {
-    var previewDiv = document.getElementById('preview');
-    previewDiv.innerHTML = '';
     var rtl = newDir == 'rtl';
-    previewWorkspace = Blockly.inject(previewDiv, {rtl: rtl});
+    previewWorkspace = Blockly.inject('preview', {rtl: rtl});
     oldDir = newDir;
   }
   var code = document.getElementById('languagePre').textContent;
@@ -481,8 +479,7 @@ function init() {
   window.addEventListener('resize', onresize);
 
   var toolbox = document.getElementById('toolbox');
-  mainWorkspace =
-      Blockly.inject(document.getElementById('blockly'), {toolbox: toolbox});
+  mainWorkspace = Blockly.inject('blockly', {toolbox: toolbox});
 
   // Create the root block.
   if ('BlocklyStorage' in window && window.location.hash.length > 1) {
diff --git a/demos/code/code.js b/demos/code/code.js
index d29ecdb33..2fed68b40 100644
--- a/demos/code/code.js
+++ b/demos/code/code.js
@@ -372,7 +372,7 @@ Code.init = function() {
   window.addEventListener('resize', onresize, false);
 
   var toolbox = document.getElementById('toolbox');
-  Code.workspace = Blockly.inject(document.getElementById('content_blocks'),
+  Code.workspace = Blockly.inject('content_blocks',
       {grid:
           {spacing: 25,
            length: 3,
diff --git a/demos/fixed/index.html b/demos/fixed/index.html
index baa3a510d..d2fa53e70 100644
--- a/demos/fixed/index.html
+++ b/demos/fixed/index.html
@@ -38,7 +38,7 @@
   </xml>
 
   <script>
-    Blockly.inject(document.getElementById('blocklyDiv'),
+    var workspace = Blockly.inject('blocklyDiv',
         {toolbox: document.getElementById('toolbox')});
   </script>
 
diff --git a/demos/generator/index.html b/demos/generator/index.html
index eadd4f6a3..f8e3dbec2 100644
--- a/demos/generator/index.html
+++ b/demos/generator/index.html
@@ -113,7 +113,7 @@
   </xml>
 
   <script>
-    var workspace = Blockly.inject(document.getElementById('blocklyDiv'),
+    var workspace = Blockly.inject('blocklyDiv',
         {toolbox: document.getElementById('toolbox')});
     Blockly.Xml.domToWorkspace(workspace,
         document.getElementById('startBlocks'));
diff --git a/demos/graph/index.html b/demos/graph/index.html
index f735fe91a..b64161580 100644
--- a/demos/graph/index.html
+++ b/demos/graph/index.html
@@ -269,7 +269,7 @@ Graph.resize = function() {
  * Initialize Blockly and the graph.  Called on page load.
  */
 Graph.init = function() {
-  Graph.workspace = Blockly.inject(document.getElementById('blocklyDiv'),
+  Graph.workspace = Blockly.inject('blocklyDiv',
       {toolbox: document.getElementById('toolbox')});
   Blockly.Xml.domToWorkspace(Graph.workspace,
       document.getElementById('startBlocks'));
diff --git a/demos/interpreter/index.html b/demos/interpreter/index.html
index 2118a03e7..59a3d5cf8 100644
--- a/demos/interpreter/index.html
+++ b/demos/interpreter/index.html
@@ -121,7 +121,7 @@
   </xml>
 
   <script>
-    var workspace = Blockly.inject(document.getElementById('blocklyDiv'),
+    var workspace = Blockly.inject('blocklyDiv',
         {toolbox: document.getElementById('toolbox')});
     Blockly.Xml.domToWorkspace(workspace,
         document.getElementById('startBlocks'));
diff --git a/demos/maxBlocks/index.html b/demos/maxBlocks/index.html
index f53f62980..86b0d360f 100644
--- a/demos/maxBlocks/index.html
+++ b/demos/maxBlocks/index.html
@@ -79,7 +79,7 @@
   </xml>
 
   <script>
-    var workspace = Blockly.inject(document.getElementById('blocklyDiv'),
+    var workspace = Blockly.inject('blocklyDiv',
         {maxBlocks: 5, toolbox: document.getElementById('toolbox')});
 
     function onchange() {
diff --git a/demos/plane/plane.js b/demos/plane/plane.js
index 38a183a09..bc2cd164d 100644
--- a/demos/plane/plane.js
+++ b/demos/plane/plane.js
@@ -262,7 +262,7 @@ Plane.init = function() {
         'width=725, initial-scale=.35, user-scalable=no');
   }
 
-  Plane.workspace = Blockly.inject(document.getElementById('blockly'),
+  Plane.workspace = Blockly.inject('blockly',
       {media: '../../media/',
        rtl: Plane.isRtl(),
        toolbox: document.getElementById('toolbox')});
diff --git a/demos/rtl/index.html b/demos/rtl/index.html
index 06d769f93..e7389fb9e 100644
--- a/demos/rtl/index.html
+++ b/demos/rtl/index.html
@@ -16,14 +16,14 @@
       font-weight: normal;
       font-size: 140%;
     }
-    #svgDiv {
+    #blocklyDiv {
       height: 600px;
       width: 800px;
     }
   </style>
   <script>
     function init() {
-      var workspace = Blockly.inject(document.getElementById('svgDiv'),
+      var workspace = Blockly.inject('blocklyDiv',
           {rtl: true, toolbox: document.getElementById('toolbox')});
       Blockly.Xml.domToWorkspace(workspace,
           document.getElementById('startBlocks'));
@@ -37,7 +37,7 @@
   <h1><a href="https://developers.google.com/blockly/">Blockly</a> &gt;
     <a href="../index.html">Demos</a> &gt; Right-to-Left</h1>
 
-  <div id="svgDiv"></div>
+  <div id="blocklyDiv"></div>
 
   <xml id="toolbox" style="display: none">
     <category name="منطق">
diff --git a/demos/storage/index.html b/demos/storage/index.html
index ca3a5176b..3d67dc4ba 100644
--- a/demos/storage/index.html
+++ b/demos/storage/index.html
@@ -80,7 +80,7 @@
   </xml>
 
   <script>
-    Blockly.inject(document.getElementById('blocklyDiv'),
+    var workspace = Blockly.inject('blocklyDiv',
         {toolbox: document.getElementById('toolbox')});
 
     // An href with #key trigers an AJAX call to retrieve saved blocks.
diff --git a/demos/toolbox/index.html b/demos/toolbox/index.html
index a975410e2..a5e10159b 100644
--- a/demos/toolbox/index.html
+++ b/demos/toolbox/index.html
@@ -341,7 +341,7 @@
   </xml>
 
   <script>
-    Blockly.inject(document.getElementById('blocklyDiv'),
+    var workspace = Blockly.inject('blocklyDiv',
         {toolbox: document.getElementById('toolbox')});
   </script>
 
diff --git a/tests/generators/index.html b/tests/generators/index.html
index c8e1e7417..8d135ab65 100644
--- a/tests/generators/index.html
+++ b/tests/generators/index.html
@@ -47,10 +47,11 @@
 <script>
 'use strict';
 
+var workspace = null;
+
 function start() {
-  var toolbox = document.getElementById('toolbox');
-  Blockly.inject(document.getElementById('svg'),
-                 {media: '../../media/', toolbox: toolbox});
+  workspace = Blockly.inject('blocklyDiv',
+      {media: '../../media/', toolbox: document.getElementById('toolbox')});
 }
 
 function loadXml() {
@@ -91,14 +92,14 @@ function fetchFile(xmlUrl) {
 function fromXml(xmlText) {
   var output = document.getElementById('importExport');
   output.value = xmlText;
-  Blockly.mainWorkspace.clear();
+  workspace.clear();
   try {
     var xmlDoc = Blockly.Xml.textToDom(xmlText);
   } catch (e) {
     alert('Error parsing XML:\n' + e);
     return;
   }
-  Blockly.Xml.domToWorkspace(Blockly.mainWorkspace, xmlDoc);
+  Blockly.Xml.domToWorkspace(workspace, xmlDoc);
 }
 
 function setOutput(text) {
@@ -109,24 +110,24 @@ function setOutput(text) {
 }
 
 function toXml() {
-  var xmlDom = Blockly.Xml.workspaceToDom(Blockly.mainWorkspace);
+  var xmlDom = Blockly.Xml.workspaceToDom(workspace);
   var xmlText = Blockly.Xml.domToPrettyText(xmlDom);
   setOutput(xmlText);
 }
 
 function toJavaScript() {
   var code = '\'use strict\';\n\n'
-  code += Blockly.JavaScript.workspaceToCode();
+  code += Blockly.JavaScript.workspaceToCode(workspace);
   setOutput(code);
 }
 
 function toPython() {
-  var code = Blockly.Python.workspaceToCode();
+  var code = Blockly.Python.workspaceToCode(workspace);
   setOutput(code);
 }
 
 function toDart() {
-  var code = Blockly.Dart.workspaceToCode();
+  var code = Blockly.Dart.workspaceToCode(workspace);
   setOutput(code);
 }
 </script>
@@ -145,15 +146,12 @@ h1 {
   font-weight: normal;
   font-size: 140%;
 }
-#svg {
+#blocklyDiv {
   float: right;
   height: 95%;
   width: 69%;
   margin-top: 5px;
 }
-.blocklySvg {
-  border: 1px solid #000;
-}
 #importExport {
   height: 100%;
   width: 100%;
@@ -162,7 +160,7 @@ h1 {
 </head>
 <body onload="start()">
 
-  <div id="svg"></div>
+  <div id="blocklyDiv"></div>
 
   <xml id="toolbox" style="display: none">
     <category name="Unit test">
diff --git a/tests/jsunit/blockly_test.js b/tests/jsunit/blockly_test.js
index e77490fe0..8dffb9dd1 100644
--- a/tests/jsunit/blockly_test.js
+++ b/tests/jsunit/blockly_test.js
@@ -38,35 +38,35 @@ function verify_DB_(msg, expected, db) {
 
 function test_DB_addConnection() {
   var db = new Blockly.ConnectionDB();
-  var o2 = {y_: 2};
+  var o2 = {y_: 2, sourceBlock_: {}};
   db.addConnection_(o2);
   verify_DB_('Adding connection #2', [o2], db);
 
-  var o4 = {y_: 4};
+  var o4 = {y_: 4, sourceBlock_: {}};
   db.addConnection_(o4);
   verify_DB_('Adding connection #4', [o2, o4], db);
 
-  var o1 = {y_: 1};
+  var o1 = {y_: 1, sourceBlock_: {}};
   db.addConnection_(o1);
   verify_DB_('Adding connection #1', [o1, o2, o4], db);
 
-  var o3a = {y_: 3};
+  var o3a = {y_: 3, sourceBlock_: {}};
   db.addConnection_(o3a);
   verify_DB_('Adding connection #3a', [o1, o2, o3a, o4], db);
 
-  var o3b = {y_: 3};
+  var o3b = {y_: 3, sourceBlock_: {}};
   db.addConnection_(o3b);
   verify_DB_('Adding connection #3b', [o1, o2, o3b, o3a, o4], db);
 }
 
 function test_DB_removeConnection() {
   var db = new Blockly.ConnectionDB();
-  var o1 = {y_: 1};
-  var o2 = {y_: 2};
-  var o3a = {y_: 3};
-  var o3b = {y_: 3};
-  var o3c = {y_: 3};
-  var o4 = {y_: 4};
+  var o1 = {y_: 1, sourceBlock_: {}};
+  var o2 = {y_: 2, sourceBlock_: {}};
+  var o3a = {y_: 3, sourceBlock_: {}};
+  var o3b = {y_: 3, sourceBlock_: {}};
+  var o3c = {y_: 3, sourceBlock_: {}};
+  var o4 = {y_: 4, sourceBlock_: {}};
   db.addConnection_(o1);
   db.addConnection_(o2);
   db.addConnection_(o3c);
diff --git a/tests/jsunit/workspace_test.js b/tests/jsunit/workspace_test.js
index 7722f9885..e8e271b9d 100644
--- a/tests/jsunit/workspace_test.js
+++ b/tests/jsunit/workspace_test.js
@@ -55,13 +55,13 @@ function test_maxBlocksWorkspace() {
   var blockA = Blockly.Block.obtain(workspace, '');
   var blockB = Blockly.Block.obtain(workspace, '');
   assertEquals('Infinite capacity.', Infinity, workspace.remainingCapacity());
-  workspace.maxBlocks = 3;
+  workspace.options.maxBlocks = 3;
   assertEquals('Three capacity.', 1, workspace.remainingCapacity());
-  workspace.maxBlocks = 2;
+  workspace.options.maxBlocks = 2;
   assertEquals('Two capacity.', 0, workspace.remainingCapacity());
-  workspace.maxBlocks = 1;
+  workspace.options.maxBlocks = 1;
   assertEquals('One capacity.', -1, workspace.remainingCapacity());
-  workspace.maxBlocks = 0;
+  workspace.options.maxBlocks = 0;
   assertEquals('Zero capacity.', -2, workspace.remainingCapacity());
   workspace.clear();
   assertEquals('Cleared capacity.', 0, workspace.remainingCapacity());
diff --git a/tests/playground.html b/tests/playground.html
index 18d96b3fb..da90cdb1e 100644
--- a/tests/playground.html
+++ b/tests/playground.html
@@ -46,7 +46,7 @@
 'use strict';
 // Depending on the URL argument, render as LTR or RTL.
 var rtl = (document.location.search == '?rtl');
-var block = null;
+var workspace = null;
 
 function enableRealtimeSpecificUi() {
   var realtimeDiv = document.getElementById('realtime');
@@ -55,7 +55,7 @@ function enableRealtimeSpecificUi() {
 
 function start() {
   var toolbox = document.getElementById('toolbox');
-  Blockly.inject(document.getElementById('blocklyDiv'),
+  workspace = Blockly.inject('blocklyDiv',
           {rtl: rtl,
            media: '../media/',
            toolbox: toolbox,
@@ -82,7 +82,7 @@ function start() {
 
 function toXml() {
   var output = document.getElementById('importExport');
-  var xml = Blockly.Xml.workspaceToDom(Blockly.mainWorkspace);
+  var xml = Blockly.Xml.workspaceToDom(workspace);
   output.value = Blockly.Xml.domToPrettyText(xml);
   output.focus();
   output.select();
@@ -91,12 +91,12 @@ function toXml() {
 function fromXml() {
   var input = document.getElementById('importExport');
   var xml = Blockly.Xml.textToDom(input.value);
-  Blockly.Xml.domToWorkspace(Blockly.mainWorkspace, xml);
+  Blockly.Xml.domToWorkspace(workspace, xml);
 }
 
 function toCode(lang) {
   var output = document.getElementById('importExport');
-  output.value = Blockly[lang].workspaceToCode();
+  output.value = Blockly[lang].workspaceToCode(workspace);
 }
 
 function airstrike(n) {
@@ -108,7 +108,7 @@ function airstrike(n) {
   }
   for (var i = 0; i < n; i++) {
     var prototype = prototypes[Math.floor(Math.random() * prototypes.length)];
-    var block = Blockly.Block.obtain(Blockly.mainWorkspace, prototype);
+    var block = Blockly.Block.obtain(workspace, prototype);
     block.initSvg();
     block.getSvgRoot().setAttribute('transform', 'translate(' +
         Math.round(Math.random() * 450 + 40) + ', ' +
@@ -126,7 +126,7 @@ function spaghetti(n) {
   xml = '<xml xmlns="http://www.w3.org/1999/xhtml">' + xml + '</xml>';
   var dom = Blockly.Xml.textToDom(xml);
   console.time('Spaghetti domToWorkspace');
-  Blockly.Xml.domToWorkspace(Blockly.mainWorkspace, dom);
+  Blockly.Xml.domToWorkspace(workspace, dom);
   console.timeEnd('Spaghetti domToWorkspace');
 }
 var spaghettiXml = [
@@ -418,7 +418,7 @@ h1 {
 
   <h1>Blockly Playground</h1>
 
-  <p><a href="javascript:void([document.getElementById('blocklyDiv').style.display = 'block', Blockly.mainWorkspace.render()])">Show</a>
+  <p><a href="javascript:void([document.getElementById('blocklyDiv').style.display = 'block', workspace.render()])">Show</a>
    - <a href="javascript:void(document.getElementById('blocklyDiv').style.display = 'none')">Hide</a></p>
 
   <script>