Merge pull request #837 from nathan/optim

Optimizations

10 files changed, 341 insertions, 488 deletions

diff --git a/blocks.js b/blocks.js
index 67324ca..d023db8 100644
--- a/blocks.js
+++ b/blocks.js
@@ -240,7 +240,7 @@ WorldMorph.prototype.customMorphs = function () {
 
 // SyntaxElementMorph inherits from Morph:
 
-SyntaxElementMorph.prototype = new Morph();
+SyntaxElementMorph.prototype = Object.create(Morph.prototype);
 SyntaxElementMorph.prototype.constructor = SyntaxElementMorph;
 SyntaxElementMorph.uber = Morph.prototype;
 
@@ -621,6 +621,10 @@ SyntaxElementMorph.prototype.topBlock = function () {
     return this;
 };
 
+// SyntaxElementMorph stepping:
+
+SyntaxElementMorph.prototype.step = null;
+
 // SyntaxElementMorph drag & drop:
 
 SyntaxElementMorph.prototype.reactToGrabOf = function (grabbedMorph) {
@@ -1417,16 +1421,19 @@ SyntaxElementMorph.prototype.labelPart = function (spec) {
                 new Point() : this.embossing;
         part.drawNew();
     } else {
-        part = new StringMorph(spec);
-        part.fontName = this.labelFontName;
-        part.fontStyle = this.labelFontStyle;
-        part.fontSize = this.fontSize;
-        part.color = new Color(255, 255, 255);
-        part.isBold = true;
-        part.shadowColor = this.color.darker(this.labelContrast);
-        part.shadowOffset = MorphicPreferences.isFlat ?
-                new Point() : this.embossing;
-        part.drawNew();
+        part = new StringMorph(
+            spec, // text
+            this.fontSize, // fontSize
+            this.labelFontStyle, // fontStyle
+            true, // bold
+            false, // italic
+            false, // isNumeric
+            MorphicPreferences.isFlat ?
+                new Point() : this.embossing, // shadowOffset
+            this.color.darker(this.labelContrast), // shadowColor
+            new Color(255, 255, 255), // color
+            this.labelFontName // fontName
+            );
     }
     return part;
 };
@@ -1937,7 +1944,7 @@ SyntaxElementMorph.prototype.endLayout = function () {
 
 // BlockMorph inherits from SyntaxElementMorph:
 
-BlockMorph.prototype = new SyntaxElementMorph();
+BlockMorph.prototype = Object.create(SyntaxElementMorph.prototype);
 BlockMorph.prototype.constructor = BlockMorph;
 BlockMorph.uber = SyntaxElementMorph.prototype;
 
@@ -2058,7 +2065,7 @@ BlockMorph.prototype.setSpec = function (spec) {
         }
         part = myself.labelPart(word);
         myself.add(part);
-        if (!(part instanceof CommandSlotMorph)) {
+        if (!(part instanceof CommandSlotMorph || part instanceof StringMorph)) {
             part.drawNew();
         }
         if (part instanceof RingMorph) {
@@ -2225,7 +2232,7 @@ BlockMorph.prototype.userMenu = function () {
     );
     if (this instanceof CommandBlockMorph && this.nextBlock()) {
         menu.addItem(
-            this.thumbnail(0.5, 60, false),
+            this.thumbnail(0.5, 60),
             function () {
                 var cpy = this.fullCopy(),
                     nb = cpy.nextBlock(),
@@ -3103,38 +3110,34 @@ BlockMorph.prototype.mouseClickLeft = function () {
 
 // BlockMorph thumbnail
 
-BlockMorph.prototype.thumbnail = function (scale, clipWidth, noShadow) {
-    var block = this.fullCopy(),
-        nb = block.nextBlock(),
+BlockMorph.prototype.thumbnail = function (scale, clipWidth) {
+    var nb = this.nextBlock(),
         fadeout = 12,
         ext,
         trgt,
         ctx,
         gradient;
-    if (nb) {nb.destroy(); }
-    if (!noShadow) {block.addShadow(); }
-    ext = block.fullBounds().extent();
-    if (!noShadow) {
-        ext = ext.subtract(this.shadowBlur *
-            (useBlurredShadows && !MorphicPreferences.isFlat ? 1 : 2));
-    }
+
+    if (nb) {nb.isVisible = false; }
+    ext = this.fullBounds().extent();
     trgt = newCanvas(new Point(
-        Math.min(ext.x * scale, clipWidth || ext.x),
+        clipWidth ? Math.min(ext.x * scale, clipWidth) : ext.x * scale,
         ext.y * scale
     ));
     ctx = trgt.getContext('2d');
     ctx.scale(scale, scale);
-    ctx.drawImage(block.fullImage(), 0, 0);
+    ctx.drawImage(this.fullImage(), 0, 0);
     // draw fade-out
-    if (trgt.width === clipWidth) {
+    if (clipWidth && ext.x * scale > clipWidth) {
         gradient = ctx.createLinearGradient(
             trgt.width / scale - fadeout,
             0,
             trgt.width / scale,
             0
         );
-        gradient.addColorStop(0, new Color(255, 255, 255, 0).toString());
-        gradient.addColorStop(1, 'white');
+        gradient.addColorStop(0, 'transparent');
+        gradient.addColorStop(1, 'black');
+        ctx.globalCompositeOperation = 'destination-out';
         ctx.fillStyle = gradient;
         ctx.fillRect(
             trgt.width / scale - fadeout,
@@ -3143,6 +3146,7 @@ BlockMorph.prototype.thumbnail = function (scale, clipWidth, noShadow) {
             trgt.height / scale
         );
     }
+    if (nb) {nb.isVisible = true; }
     return trgt;
 };
 
@@ -3262,7 +3266,7 @@ BlockMorph.prototype.snap = function () {
 
 // CommandBlockMorph inherits from BlockMorph:
 
-CommandBlockMorph.prototype = new BlockMorph();
+CommandBlockMorph.prototype = Object.create(BlockMorph.prototype);
 CommandBlockMorph.prototype.constructor = CommandBlockMorph;
 CommandBlockMorph.uber = BlockMorph.prototype;
 
@@ -3942,7 +3946,7 @@ CommandBlockMorph.prototype.drawBottomRightEdge = function (context) {
 
 // HatBlockMorph inherits from CommandBlockMorph:
 
-HatBlockMorph.prototype = new CommandBlockMorph();
+HatBlockMorph.prototype = Object.create(CommandBlockMorph.prototype);
 HatBlockMorph.prototype.constructor = HatBlockMorph;
 HatBlockMorph.uber = CommandBlockMorph.prototype;
 
@@ -4120,7 +4124,7 @@ HatBlockMorph.prototype.drawTopLeftEdge = function (context) {
 
 // ReporterBlockMorph inherits from BlockMorph:
 
-ReporterBlockMorph.prototype = new BlockMorph();
+ReporterBlockMorph.prototype = Object.create(BlockMorph.prototype);
 ReporterBlockMorph.prototype.constructor = ReporterBlockMorph;
 ReporterBlockMorph.uber = BlockMorph.prototype;
 
@@ -4644,7 +4648,7 @@ ReporterBlockMorph.prototype.drawDiamond = function (context) {
 
 // RingMorph inherits from ReporterBlockMorph:
 
-RingMorph.prototype = new ReporterBlockMorph();
+RingMorph.prototype = Object.create(ReporterBlockMorph.prototype);
 RingMorph.prototype.constructor = RingMorph;
 RingMorph.uber = ReporterBlockMorph.prototype;
 
@@ -4781,7 +4785,7 @@ RingMorph.prototype.fixBlockColor = function (nearest, isForced) {
 
 // ScriptsMorph inherits from FrameMorph:
 
-ScriptsMorph.prototype = new FrameMorph();
+ScriptsMorph.prototype = Object.create(FrameMorph.prototype);
 ScriptsMorph.prototype.constructor = ScriptsMorph;
 ScriptsMorph.uber = FrameMorph.prototype;
 
@@ -5321,7 +5325,7 @@ ScriptsMorph.prototype.reactToDropOf = function (droppedMorph, hand) {
 
 // ArgMorph inherits from SyntaxElementMorph:
 
-ArgMorph.prototype = new SyntaxElementMorph();
+ArgMorph.prototype = Object.create(SyntaxElementMorph.prototype);
 ArgMorph.prototype.constructor = ArgMorph;
 ArgMorph.uber = SyntaxElementMorph.prototype;
 
@@ -5434,7 +5438,7 @@ ArgMorph.prototype.isEmptySlot = function () {
 
 // CommandSlotMorph inherits from ArgMorph:
 
-CommandSlotMorph.prototype = new ArgMorph();
+CommandSlotMorph.prototype = Object.create(ArgMorph.prototype);
 CommandSlotMorph.prototype.constructor = CommandSlotMorph;
 CommandSlotMorph.uber = ArgMorph.prototype;
 
@@ -5884,7 +5888,7 @@ CommandSlotMorph.prototype.drawEdges = function (context) {
 
 // RingCommandSlotMorph inherits from CommandSlotMorph:
 
-RingCommandSlotMorph.prototype = new CommandSlotMorph();
+RingCommandSlotMorph.prototype = Object.create(CommandSlotMorph.prototype);
 RingCommandSlotMorph.prototype.constructor = RingCommandSlotMorph;
 RingCommandSlotMorph.uber = CommandSlotMorph.prototype;
 
@@ -6040,7 +6044,7 @@ RingCommandSlotMorph.prototype.drawFlat = function (context) {
 
 // CSlotMorph inherits from CommandSlotMorph:
 
-CSlotMorph.prototype = new CommandSlotMorph();
+CSlotMorph.prototype = Object.create(CommandSlotMorph.prototype);
 CSlotMorph.prototype.constructor = CSlotMorph;
 CSlotMorph.uber = CommandSlotMorph.prototype;
 
@@ -6463,7 +6467,7 @@ CSlotMorph.prototype.drawBottomEdge = function (context) {
 
 // InputSlotMorph inherits from ArgMorph:
 
-InputSlotMorph.prototype = new ArgMorph();
+InputSlotMorph.prototype = Object.create(ArgMorph.prototype);
 InputSlotMorph.prototype.constructor = InputSlotMorph;
 InputSlotMorph.uber = ArgMorph.prototype;
 
@@ -6917,7 +6921,8 @@ InputSlotMorph.prototype.setChoices = function (dict, readonly) {
 // InputSlotMorph layout:
 
 InputSlotMorph.prototype.fixLayout = function () {
-    var contents = this.contents(),
+    var width, height, arrowWidth,
+        contents = this.contents(),
         arrow = this.arrow();
 
     contents.isNumeric = this.isNumeric;
@@ -6934,35 +6939,32 @@ InputSlotMorph.prototype.fixLayout = function () {
         arrow.setSize(this.fontSize);
         arrow.show();
     } else {
-        arrow.setSize(0);
         arrow.hide();
     }
-    this.setHeight(
-        contents.height()
-            + this.edge * 2
-            // + this.typeInPadding * 2
-    );
+    arrowWidth = arrow.isVisible ? arrow.width() : 0;
+
+    height = contents.height() + this.edge * 2; // + this.typeInPadding * 2
     if (this.isNumeric) {
-        this.setWidth(contents.width()
-            + Math.floor(arrow.width() * 0.5)
-            + this.height()
-            + this.typeInPadding * 2
-            );
+        width = contents.width()
+            + Math.floor(arrowWidth * 0.5)
+            + height
+            + this.typeInPadding * 2;
     } else {
-        this.setWidth(Math.max(
+        width = Math.max(
             contents.width()
-                + arrow.width()
+                + arrowWidth
                 + this.edge * 2
                 + this.typeInPadding * 2,
             contents.rawHeight ? // single vs. multi-line contents
-                        contents.rawHeight() + arrow.width()
-                                : contents.height() / 1.2 + arrow.width(),
+                        contents.rawHeight() + arrowWidth
+                                : contents.height() / 1.2 + arrowWidth,
             this.minWidth // for text-type slots
-        ));
+        );
     }
+    this.setExtent(new Point(width, height));
     if (this.isNumeric) {
         contents.setPosition(new Point(
-            Math.floor(this.height() / 2),
+            Math.floor(height / 2),
             this.edge
         ).add(new Point(this.typeInPadding, 0)).add(this.position()));
     } else {
@@ -6972,10 +6974,12 @@ InputSlotMorph.prototype.fixLayout = function () {
         ).add(new Point(this.typeInPadding, 0)).add(this.position()));
     }
 
-    arrow.setPosition(new Point(
-        this.right() - arrow.width() - this.edge,
-        contents.top()
-    ));
+    if (arrow.isVisible) {
+        arrow.setPosition(new Point(
+            this.right() - arrowWidth - this.edge,
+            contents.top()
+        ));
+    }
 
     if (this.parent) {
         if (this.parent.fixLayout) {
@@ -7399,7 +7403,7 @@ InputSlotMorph.prototype.drawRoundBorder = function (context) {
 
 // TemplateSlotMorph inherits from ArgMorph:
 
-TemplateSlotMorph.prototype = new ArgMorph();
+TemplateSlotMorph.prototype = Object.create(ArgMorph.prototype);
 TemplateSlotMorph.prototype.constructor = TemplateSlotMorph;
 TemplateSlotMorph.uber = ArgMorph.prototype;
 
@@ -7503,7 +7507,7 @@ TemplateSlotMorph.prototype.drawRounded = ReporterBlockMorph
 
 // BooleanSlotMorph inherits from ArgMorph:
 
-BooleanSlotMorph.prototype = new ArgMorph();
+BooleanSlotMorph.prototype = Object.create(ArgMorph.prototype);
 BooleanSlotMorph.prototype.constructor = BooleanSlotMorph;
 BooleanSlotMorph.uber = ArgMorph.prototype;
 
@@ -7660,7 +7664,7 @@ BooleanSlotMorph.prototype.isEmptySlot = function () {
 
 // ArrowMorph inherits from Morph:
 
-ArrowMorph.prototype = new Morph();
+ArrowMorph.prototype = Object.create(Morph.prototype);
 ArrowMorph.prototype.constructor = ArrowMorph;
 ArrowMorph.uber = Morph.prototype;
 
@@ -7730,7 +7734,7 @@ ArrowMorph.prototype.drawNew = function () {
 
 // TextSlotMorph inherits from InputSlotMorph:
 
-TextSlotMorph.prototype = new InputSlotMorph();
+TextSlotMorph.prototype = Object.create(InputSlotMorph.prototype);
 TextSlotMorph.prototype.constructor = TextSlotMorph;
 TextSlotMorph.uber = InputSlotMorph.prototype;
 
@@ -7813,7 +7817,7 @@ TextSlotMorph.prototype.layoutChanged = function () {
 
 // SymbolMorph inherits from Morph:
 
-SymbolMorph.prototype = new Morph();
+SymbolMorph.prototype = Object.create(Morph.prototype);
 SymbolMorph.prototype.constructor = SymbolMorph;
 SymbolMorph.uber = Morph.prototype;
 
@@ -9106,7 +9110,7 @@ SymbolMorph.prototype.drawSymbolRobot = function (canvas, color) {
 
 // ColorSlotMorph  inherits from ArgMorph:
 
-ColorSlotMorph.prototype = new ArgMorph();
+ColorSlotMorph.prototype = Object.create(ArgMorph.prototype);
 ColorSlotMorph.prototype.constructor = ColorSlotMorph;
 ColorSlotMorph.uber = ArgMorph.prototype;
 
@@ -9214,7 +9218,7 @@ ColorSlotMorph.prototype.drawRectBorder =
 
 // BlockHighlightMorph inherits from Morph:
 
-BlockHighlightMorph.prototype = new Morph();
+BlockHighlightMorph.prototype = Object.create(Morph.prototype);
 BlockHighlightMorph.prototype.constructor = BlockHighlightMorph;
 BlockHighlightMorph.uber = Morph.prototype;
 
@@ -9239,7 +9243,7 @@ function BlockHighlightMorph() {
 
 // MultiArgMorph  inherits from ArgMorph:
 
-MultiArgMorph.prototype = new ArgMorph();
+MultiArgMorph.prototype = Object.create(ArgMorph.prototype);
 MultiArgMorph.prototype.constructor = MultiArgMorph;
 MultiArgMorph.uber = ArgMorph.prototype;
 
@@ -9669,7 +9673,7 @@ MultiArgMorph.prototype.isEmptySlot = function () {
 
 // ArgLabelMorph  inherits from ArgMorph:
 
-ArgLabelMorph.prototype = new ArgMorph();
+ArgLabelMorph.prototype = Object.create(ArgMorph.prototype);
 ArgLabelMorph.prototype.constructor = ArgLabelMorph;
 ArgLabelMorph.uber = ArgMorph.prototype;
 
@@ -9799,7 +9803,7 @@ ArgLabelMorph.prototype.isEmptySlot = function () {
 
 // FunctionSlotMorph inherits from ArgMorph:
 
-FunctionSlotMorph.prototype = new ArgMorph();
+FunctionSlotMorph.prototype = Object.create(ArgMorph.prototype);
 FunctionSlotMorph.prototype.constructor = FunctionSlotMorph;
 FunctionSlotMorph.uber = ArgMorph.prototype;
 
@@ -10180,7 +10184,7 @@ FunctionSlotMorph.prototype.drawDiamond = function (context) {
 
 // ReporterSlotMorph inherits from FunctionSlotMorph:
 
-ReporterSlotMorph.prototype = new FunctionSlotMorph();
+ReporterSlotMorph.prototype = Object.create(FunctionSlotMorph.prototype);
 ReporterSlotMorph.prototype.constructor = ReporterSlotMorph;
 ReporterSlotMorph.uber = FunctionSlotMorph.prototype;
 
@@ -10263,7 +10267,7 @@ ReporterSlotMorph.prototype.fixLayout = function () {
 
 // ReporterSlotMorph inherits from FunctionSlotMorph:
 
-RingReporterSlotMorph.prototype = new ReporterSlotMorph();
+RingReporterSlotMorph.prototype = Object.create(ReporterSlotMorph.prototype);
 RingReporterSlotMorph.prototype.constructor = RingReporterSlotMorph;
 RingReporterSlotMorph.uber = ReporterSlotMorph.prototype;
 
@@ -10651,7 +10655,7 @@ RingReporterSlotMorph.prototype.drawDiamond = function (context) {
 
 // CommentMorph inherits from BoxMorph:
 
-CommentMorph.prototype = new BoxMorph();
+CommentMorph.prototype = Object.create(BoxMorph.prototype);
 CommentMorph.prototype.constructor = CommentMorph;
 CommentMorph.uber = BoxMorph.prototype;
 
diff --git a/byob.js b/byob.js
index 1c2cfee..32d8969 100644
--- a/byob.js
+++ b/byob.js
@@ -379,7 +379,7 @@ CustomBlockDefinition.prototype.scriptsPicture = function () {
 
 // CustomCommandBlockMorph inherits from CommandBlockMorph:
 
-CustomCommandBlockMorph.prototype = new CommandBlockMorph();
+CustomCommandBlockMorph.prototype = Object.create(CommandBlockMorph.prototype);
 CustomCommandBlockMorph.prototype.constructor = CustomCommandBlockMorph;
 CustomCommandBlockMorph.uber = CommandBlockMorph.prototype;
 
@@ -896,7 +896,7 @@ CustomCommandBlockMorph.prototype.alternatives = function () {
 
 // CustomReporterBlockMorph inherits from ReporterBlockMorph:
 
-CustomReporterBlockMorph.prototype = new ReporterBlockMorph();
+CustomReporterBlockMorph.prototype = Object.create(ReporterBlockMorph.prototype);
 CustomReporterBlockMorph.prototype.constructor = CustomReporterBlockMorph;
 CustomReporterBlockMorph.uber = ReporterBlockMorph.prototype;
 
@@ -1028,7 +1028,7 @@ CustomReporterBlockMorph.prototype.alternatives
 
 // JaggedBlockMorph inherits from ReporterBlockMorph:
 
-JaggedBlockMorph.prototype = new ReporterBlockMorph();
+JaggedBlockMorph.prototype = Object.create(ReporterBlockMorph.prototype);
 JaggedBlockMorph.prototype.constructor = JaggedBlockMorph;
 JaggedBlockMorph.uber = ReporterBlockMorph.prototype;
 
@@ -1177,7 +1177,7 @@ JaggedBlockMorph.prototype.drawEdges = function (context) {
 
 // BlockDialogMorph inherits from DialogBoxMorph:
 
-BlockDialogMorph.prototype = new DialogBoxMorph();
+BlockDialogMorph.prototype = Object.create(DialogBoxMorph.prototype);
 BlockDialogMorph.prototype.constructor = BlockDialogMorph;
 BlockDialogMorph.uber = DialogBoxMorph.prototype;
 
@@ -1624,7 +1624,7 @@ BlockDialogMorph.prototype.fixLayout = function () {
 
 // BlockEditorMorph inherits from DialogBoxMorph:
 
-BlockEditorMorph.prototype = new DialogBoxMorph();
+BlockEditorMorph.prototype = Object.create(DialogBoxMorph.prototype);
 BlockEditorMorph.prototype.constructor = BlockEditorMorph;
 BlockEditorMorph.uber = DialogBoxMorph.prototype;
 
@@ -1936,7 +1936,7 @@ BlockEditorMorph.prototype.fixLayout = function () {
 
 // PrototypeHatBlockMorph inherits from HatBlockMorph:
 
-PrototypeHatBlockMorph.prototype = new HatBlockMorph();
+PrototypeHatBlockMorph.prototype = Object.create(HatBlockMorph.prototype);
 PrototypeHatBlockMorph.prototype.constructor = PrototypeHatBlockMorph;
 PrototypeHatBlockMorph.uber = HatBlockMorph.prototype;
 
@@ -2146,7 +2146,7 @@ BlockLabelFragment.prototype.setSingleInputType = function (type) {
 
 // BlockLabelFragmentMorph inherits from StringMorph:
 
-BlockLabelFragmentMorph.prototype = new StringMorph();
+BlockLabelFragmentMorph.prototype = Object.create(StringMorph.prototype);
 BlockLabelFragmentMorph.prototype.constructor = BlockLabelFragmentMorph;
 BlockLabelFragmentMorph.uber = StringMorph.prototype;
 
@@ -2268,7 +2268,7 @@ BlockLabelFragmentMorph.prototype.userMenu = function () {
 
 // BlockLabelPlaceHolderMorph inherits from StringMorph:
 
-BlockLabelPlaceHolderMorph.prototype = new StringMorph();
+BlockLabelPlaceHolderMorph.prototype = Object.create(StringMorph.prototype);
 BlockLabelPlaceHolderMorph.prototype.constructor = BlockLabelPlaceHolderMorph;
 BlockLabelPlaceHolderMorph.uber = StringMorph.prototype;
 
@@ -2396,7 +2396,7 @@ BlockLabelPlaceHolderMorph.prototype.updateBlockLabel
 
 // BlockInputFragmentMorph inherits from TemplateSlotMorph:
 
-BlockInputFragmentMorph.prototype = new TemplateSlotMorph();
+BlockInputFragmentMorph.prototype = Object.create(TemplateSlotMorph.prototype);
 BlockInputFragmentMorph.prototype.constructor = BlockInputFragmentMorph;
 BlockInputFragmentMorph.uber = TemplateSlotMorph.prototype;
 
@@ -2426,7 +2426,7 @@ BlockInputFragmentMorph.prototype.updateBlockLabel
 
 // InputSlotDialogMorph inherits from DialogBoxMorph:
 
-InputSlotDialogMorph.prototype = new DialogBoxMorph();
+InputSlotDialogMorph.prototype = Object.create(DialogBoxMorph.prototype);
 InputSlotDialogMorph.prototype.constructor = InputSlotDialogMorph;
 InputSlotDialogMorph.uber = DialogBoxMorph.prototype;
 
@@ -3026,7 +3026,7 @@ InputSlotDialogMorph.prototype.show = function () {
 
 // VariableDialogMorph inherits from DialogBoxMorph:
 
-VariableDialogMorph.prototype = new DialogBoxMorph();
+VariableDialogMorph.prototype = Object.create(DialogBoxMorph.prototype);
 VariableDialogMorph.prototype.constructor = VariableDialogMorph;
 VariableDialogMorph.uber = DialogBoxMorph.prototype;
 
@@ -3145,7 +3145,7 @@ VariableDialogMorph.prototype.fixLayout = function () {
 
 // BlockExportDialogMorph inherits from DialogBoxMorph:
 
-BlockExportDialogMorph.prototype = new DialogBoxMorph();
+BlockExportDialogMorph.prototype = Object.create(DialogBoxMorph.prototype);
 BlockExportDialogMorph.prototype.constructor = BlockExportDialogMorph;
 BlockExportDialogMorph.uber = DialogBoxMorph.prototype;
 
@@ -3327,7 +3327,7 @@ BlockExportDialogMorph.prototype.fixLayout
 // BlockImportDialogMorph inherits from DialogBoxMorph
 // and pseudo-inherits from BlockExportDialogMorph:
 
-BlockImportDialogMorph.prototype = new DialogBoxMorph();
+BlockImportDialogMorph.prototype = Object.create(DialogBoxMorph.prototype);
 BlockImportDialogMorph.prototype.constructor = BlockImportDialogMorph;
 BlockImportDialogMorph.uber = DialogBoxMorph.prototype;
 
diff --git a/gui.js b/gui.js
index 026a12c..89e2d89 100644
--- a/gui.js
+++ b/gui.js
@@ -88,7 +88,7 @@ var JukeboxMorph;
 
 // IDE_Morph inherits from Morph:
 
-IDE_Morph.prototype = new Morph();
+IDE_Morph.prototype = Object.create(Morph.prototype);
 IDE_Morph.prototype.constructor = IDE_Morph;
 IDE_Morph.uber = Morph.prototype;
 
@@ -4274,7 +4274,7 @@ IDE_Morph.prototype.prompt = function (message, callback, choices, key) {
 
 // ProjectDialogMorph inherits from DialogBoxMorph:
 
-ProjectDialogMorph.prototype = new DialogBoxMorph();
+ProjectDialogMorph.prototype = Object.create(DialogBoxMorph.prototype);
 ProjectDialogMorph.prototype.constructor = ProjectDialogMorph;
 ProjectDialogMorph.uber = DialogBoxMorph.prototype;
 
@@ -5181,7 +5181,7 @@ ProjectDialogMorph.prototype.fixLayout = function () {
 
 // SpriteIconMorph inherits from ToggleButtonMorph (Widgets)
 
-SpriteIconMorph.prototype = new ToggleButtonMorph();
+SpriteIconMorph.prototype = Object.create(ToggleButtonMorph.prototype);
 SpriteIconMorph.prototype.constructor = SpriteIconMorph;
 SpriteIconMorph.uber = ToggleButtonMorph.prototype;
 
@@ -5571,7 +5571,7 @@ SpriteIconMorph.prototype.copySound = function (sound) {
 // CostumeIconMorph inherits from ToggleButtonMorph (Widgets)
 // ... and copies methods from SpriteIconMorph
 
-CostumeIconMorph.prototype = new ToggleButtonMorph();
+CostumeIconMorph.prototype = Object.create(ToggleButtonMorph.prototype);
 CostumeIconMorph.prototype.constructor = CostumeIconMorph;
 CostumeIconMorph.uber = ToggleButtonMorph.prototype;
 
@@ -5782,7 +5782,7 @@ CostumeIconMorph.prototype.prepareToBeGrabbed = function () {
 // TurtleIconMorph inherits from ToggleButtonMorph (Widgets)
 // ... and copies methods from SpriteIconMorph
 
-TurtleIconMorph.prototype = new ToggleButtonMorph();
+TurtleIconMorph.prototype = Object.create(ToggleButtonMorph.prototype);
 TurtleIconMorph.prototype.constructor = TurtleIconMorph;
 TurtleIconMorph.uber = ToggleButtonMorph.prototype;
 
@@ -5965,7 +5965,7 @@ TurtleIconMorph.prototype.userMenu = function () {
 
 // WardrobeMorph inherits from ScrollFrameMorph
 
-WardrobeMorph.prototype = new ScrollFrameMorph();
+WardrobeMorph.prototype = Object.create(ScrollFrameMorph.prototype);
 WardrobeMorph.prototype.constructor = WardrobeMorph;
 WardrobeMorph.uber = ScrollFrameMorph.prototype;
 
@@ -6148,7 +6148,7 @@ WardrobeMorph.prototype.reactToDropOf = function (icon) {
 // SoundIconMorph inherits from ToggleButtonMorph (Widgets)
 // ... and copies methods from SpriteIconMorph
 
-SoundIconMorph.prototype = new ToggleButtonMorph();
+SoundIconMorph.prototype = Object.create(ToggleButtonMorph.prototype);
 SoundIconMorph.prototype.constructor = SoundIconMorph;
 SoundIconMorph.uber = ToggleButtonMorph.prototype;
 
@@ -6356,7 +6356,7 @@ SoundIconMorph.prototype.prepareToBeGrabbed = function () {
 
 // JukeboxMorph instance creation
 
-JukeboxMorph.prototype = new ScrollFrameMorph();
+JukeboxMorph.prototype = Object.create(ScrollFrameMorph.prototype);
 JukeboxMorph.prototype.constructor = JukeboxMorph;
 JukeboxMorph.uber = ScrollFrameMorph.prototype;
 
diff --git a/lists.js b/lists.js
index bd856fe..769b8b3 100644
--- a/lists.js
+++ b/lists.js
@@ -363,7 +363,7 @@ List.prototype.equalTo = function (other) {
 
 // ListWatcherMorph inherits from BoxMorph:
 
-ListWatcherMorph.prototype = new BoxMorph();
+ListWatcherMorph.prototype = Object.create(BoxMorph.prototype);
 ListWatcherMorph.prototype.constructor = ListWatcherMorph;
 ListWatcherMorph.uber = BoxMorph.prototype;
 
@@ -388,6 +388,13 @@ ListWatcherMorph.prototype.init = function (list, parentCell) {
     this.lastCell = null;
     this.parentCell = parentCell || null; // for circularity detection
 
+    ListWatcherMorph.uber.init.call(
+        this,
+        SyntaxElementMorph.prototype.rounding,
+        1.000001, // shadow bug in Chrome,
+        new Color(120, 120, 120)
+    );
+
     // elements declarations
     this.label = new StringMorph(
         localize('length: ') + this.list.length(),
@@ -436,13 +443,6 @@ ListWatcherMorph.prototype.init = function (list, parentCell) {
     this.plusButton.drawNew();
     this.plusButton.fixLayout();
 
-    ListWatcherMorph.uber.init.call(
-        this,
-        SyntaxElementMorph.prototype.rounding,
-        1.000001, // shadow bug in Chrome,
-        new Color(120, 120, 120)
-    );
-
     this.color = new Color(220, 220, 220);
     this.isDraggable = true;
     this.setExtent(new Point(80, 70).multiplyBy(
@@ -634,6 +634,7 @@ ListWatcherMorph.prototype.setStartIndex = function (index) {
 };
 
 ListWatcherMorph.prototype.fixLayout = function () {
+    if (!this.label) return;
     Morph.prototype.trackChanges = false;
     if (this.frame) {
         this.arrangeCells();
diff --git a/morphic.js b/morphic.js
index 2850e32..e4df8f0 100644
--- a/morphic.js
+++ b/morphic.js
@@ -528,7 +528,7 @@
     whose "isTemplate" flag is false, in other words: a non-template.
 
     When creating a copy from a template, the copy's
-    
+
         reactToTemplateCopy
 
     is invoked, if it is present.
@@ -829,12 +829,11 @@
         };
 
     If your new morph stores or references other morphs outside of the
-    submorph tree in other properties, be sure to also override the
-    default
+    submorph tree in other properties, you may need to override the default
 
-        copyRecordingReferences()
+        updateReferences()
 
-    method accordingly if you want it to support duplication.
+    method if you want it to support duplication.
 
 
     (6) development and user modes
@@ -1243,19 +1242,9 @@ function getDocumentPositionOf(aDOMelement) {
     return pos;
 }
 
-function clone(target) {
-    // answer a new instance of target's type
-    if (typeof target === 'object') {
-        var Clone = function () {nop(); };
-        Clone.prototype = target;
-        return new Clone();
-    }
-    return target;
-}
-
 function copy(target) {
     // answer a shallow copy of target
-    var value, c, property;
+    var value, c, property, keys, l, i;
 
     if (typeof target !== 'object') {
         return target;
@@ -1266,18 +1255,16 @@ function copy(target) {
     }
     if (target instanceof target.constructor &&
             target.constructor !== Object) {
-        c = clone(target.constructor.prototype);
-        for (property in target) {
-            if (Object.prototype.hasOwnProperty.call(target, property)) {
-                c[property] = target[property];
-            }
+        c = Object.create(target.constructor.prototype);
+        keys = Object.keys(target);
+        for (l = keys.length, i = 0; i < l; ++i) {
+            property = keys[i];
+            c[property] = target[property];
         }
     } else {
         c = {};
         for (property in target) {
-            if (!c[property]) {
-                c[property] = target[property];
-            }
+            c[property] = target[property];
         }
     }
     return c;
@@ -2171,7 +2158,7 @@ var TextMorph;
 
 // Morph inherits from Node:
 
-Morph.prototype = new Node();
+Morph.prototype = Object.create(Node.prototype);
 Morph.prototype.constructor = Morph;
 Morph.uber = Node.prototype;
 
@@ -2212,7 +2199,7 @@ function Morph() {
 
 // Morph initialization:
 
-Morph.prototype.init = function () {
+Morph.prototype.init = function (noDraw) {
     Morph.uber.init.call(this);
     this.isMorph = true;
     this.bounds = new Rectangle(0, 0, 50, 40);
@@ -2225,7 +2212,7 @@ Morph.prototype.init = function () {
     this.isTemplate = false;
     this.acceptsDrops = false;
     this.noticesTransparentClick = false;
-    this.drawNew();
+    if (!noDraw) { this.drawNew(); }
     this.fps = 0;
     this.customContextMenu = null;
     this.lastTime = Date.now();
@@ -2411,19 +2398,16 @@ Morph.prototype.visibleBounds = function () {
 // Morph accessing - simple changes:
 
 Morph.prototype.moveBy = function (delta) {
-    this.changed();
-    this.bounds = this.bounds.translateBy(delta);
-    this.children.forEach(function (child) {
-        child.moveBy(delta);
-    });
-    this.changed();
+    this.fullChanged();
+    this.silentMoveBy(delta);
+    this.fullChanged();
 };
 
 Morph.prototype.silentMoveBy = function (delta) {
     this.bounds = this.bounds.translateBy(delta);
-    this.children.forEach(function (child) {
-        child.silentMoveBy(delta);
-    });
+    for (var children = this.children, i = children.length; i--;) {
+        children[i].silentMoveBy(delta);
+    }
 };
 
 Morph.prototype.setPosition = function (aPoint) {
@@ -2899,7 +2883,7 @@ Morph.prototype.fullChanged = function () {
 };
 
 Morph.prototype.childChanged = function () {
-    // react to a  change in one of my children,
+    // react to a change in one of my children,
     // default is to just pass this message on upwards
     // override this method for Morphs that need to adjust accordingly
     if (this.parent) {
@@ -3031,63 +3015,98 @@ Morph.prototype.isTransparentAt = function (aPoint) {
 
 // Morph duplicating:
 
-Morph.prototype.copy = function () {
-    var c = copy(this);
-    c.parent = null;
-    c.children = [];
-    c.bounds = this.bounds.copy();
-    return c;
-};
+(function () {
+    // don't overwrite the global Map with AssociativeMap
+    var Map = window.Map || AssociativeMap;
 
-Morph.prototype.fullCopy = function () {
-    /*
-    Produce a copy of me with my entire tree of submorphs. Morphs
-    mentioned more than once are all directed to a single new copy.
-    Other properties are also *shallow* copied, so you must override
-    to deep copy Arrays and (complex) Objects
-    */
-    var dict = {}, c;
-    c = this.copyRecordingReferences(dict);
-    c.forAllChildren(function (m) {
-        m.updateReferences(dict);
-    });
-    return c;
-};
+    Morph.prototype.copy = function () {
+        var c = copy(this);
+        c.parent = null;
+        c.children = [];
+        c.bounds = this.bounds.copy();
+        return c;
+    };
 
-Morph.prototype.copyRecordingReferences = function (dict) {
-    /*
-    Recursively copy this entire composite morph, recording the
-    correspondence between old and new morphs in the given dictionary.
-    This dictionary will be used to update intra-composite references
-    in the copy. See updateReferences().
-    Note: This default implementation copies ONLY morphs in the
-    submorph hierarchy. If a morph stores morphs in other properties
-    that it wants to copy, then it should override this method to do so.
-    The same goes for morphs that contain other complex data that
-    should be copied when the morph is duplicated.
-    */
-    var c = this.copy();
-    dict[this] = c;
-    this.children.forEach(function (m) {
-        c.add(m.copyRecordingReferences(dict));
-    });
-    return c;
-};
+    Morph.prototype.fullCopy = function () {
+        /*
+        Produce a copy of me with my entire tree of submorphs. Morphs
+        mentioned more than once are all directed to a single new copy.
+        Other properties are also *shallow* copied, so you must override
+        to deep copy Arrays and (complex) Objects
+        */
+        var map = new Map(), c;
+        c = this.copyRecordingReferences(map);
+        c.forAllChildren(function (m) {
+            m.updateReferences(map);
+        });
+        return c;
+    };
 
-Morph.prototype.updateReferences = function (dict) {
-    /*
-    Update intra-morph references within a composite morph that has
-    been copied. For example, if a button refers to morph X in the
-    orginal composite then the copy of that button in the new composite
-    should refer to the copy of X in new composite, not the original X.
-    */
-    var property;
-    for (property in this) {
-        if (this[property] && this[property].isMorph && dict[property]) {
-            this[property] = dict[property];
+    Morph.prototype.copyRecordingReferences = function (map) {
+        /*
+        Recursively copy this entire composite morph, recording the
+        correspondence between old and new morphs in the given dictionary.
+        This dictionary will be used to update intra-composite references
+        in the copy. See updateReferences().
+
+        Note: This default implementation copies ONLY morphs. If a morph
+        stores morphs in other properties that it wants to copy, then it
+        should override this method to do so. The same goes for morphs that
+        contain other complex data that should be copied when the morph is
+        duplicated.
+        */
+        var c = this.copy();
+        map.set(this, c);
+        this.children.forEach(function (m) {
+            c.add(m.copyRecordingReferences(map));
+        });
+        return c;
+    };
+
+    Morph.prototype.updateReferences = function (map) {
+        /*
+        Update intra-morph references within a composite morph that has
+        been copied. For example, if a button refers to morph X in the
+        orginal composite then the copy of that button in the new composite
+        should refer to the copy of X in new composite, not the original X.
+        */
+        var property, value, reference;
+        for (var properties = Object.keys(this), l = properties.length, i = 0; i < l; ++i) {
+            property = properties[i];
+            value = this[property];
+            if (value && value.isMorph) {
+                reference = map.get(value);
+                if (reference) this[property] = reference;
+            }
         }
+    };
+
+    // associative array fallback for Map
+
+    function AssociativeMap() {
+        this.keys = [];
+        this.values = [];
     }
-};
+
+    AssociativeMap.prototype.get = function(key) {
+        for (var keys = this.keys, i = keys.length; i--;) {
+            if (keys[i] === key) return this.values[i];
+        }
+        return undefined;
+    };
+
+    AssociativeMap.prototype.set = function(key, value) {
+        for (var keys = this.keys, i = keys.length; i--;) {
+            if (keys[i] === key) {
+                this.values[i] = value;
+                return;
+            }
+        }
+        keys.push(key);
+        this.values.push(value);
+    };
+
+}());
 
 // Morph dragging and dropping:
 
@@ -3155,9 +3174,7 @@ Morph.prototype.slideBackTo = function (situation, inSteps) {
 
     this.fps = 0;
     this.step = function () {
-        myself.fullChanged();
-        myself.silentMoveBy(new Point(xStep, yStep));
-        myself.fullChanged();
+        myself.moveBy(new Point(xStep, yStep));
         stepCount += 1;
         if (stepCount === steps) {
             situation.origin.add(myself);
@@ -3696,7 +3713,7 @@ Morph.prototype.overlappingImage = function (otherMorph) {
 
 // ShadowMorph inherits from Morph:
 
-ShadowMorph.prototype = new Morph();
+ShadowMorph.prototype = Object.create(Morph.prototype);
 ShadowMorph.prototype.constructor = ShadowMorph;
 ShadowMorph.uber = Morph.prototype;
 
@@ -3712,7 +3729,7 @@ function ShadowMorph() {
 
 // HandleMorph inherits from Morph:
 
-HandleMorph.prototype = new Morph();
+HandleMorph.prototype = Object.create(Morph.prototype);
 HandleMorph.prototype.constructor = HandleMorph;
 HandleMorph.uber = Morph.prototype;
 
@@ -3923,20 +3940,6 @@ HandleMorph.prototype.mouseLeave = function () {
     this.changed();
 };
 
-// HandleMorph duplicating:
-
-HandleMorph.prototype.copyRecordingReferences = function (dict) {
-    // inherited, see comment in Morph
-    var c = HandleMorph.uber.copyRecordingReferences.call(
-        this,
-        dict
-    );
-    if (c.target && dict[this.target]) {
-        c.target = (dict[this.target]);
-    }
-    return c;
-};
-
 // HandleMorph menu:
 
 HandleMorph.prototype.attach = function () {
@@ -3967,7 +3970,7 @@ var PenMorph;
 
 // PenMorph inherits from Morph:
 
-PenMorph.prototype = new Morph();
+PenMorph.prototype = Object.create(Morph.prototype);
 PenMorph.prototype.constructor = PenMorph;
 PenMorph.uber = Morph.prototype;
 
@@ -4199,7 +4202,7 @@ var ColorPaletteMorph;
 
 // ColorPaletteMorph inherits from Morph:
 
-ColorPaletteMorph.prototype = new Morph();
+ColorPaletteMorph.prototype = Object.create(Morph.prototype);
 ColorPaletteMorph.prototype.constructor = ColorPaletteMorph;
 ColorPaletteMorph.uber = Morph.prototype;
 
@@ -4260,20 +4263,6 @@ ColorPaletteMorph.prototype.updateTarget = function () {
     }
 };
 
-// ColorPaletteMorph duplicating:
-
-ColorPaletteMorph.prototype.copyRecordingReferences = function (dict) {
-    // inherited, see comment in Morph
-    var c = ColorPaletteMorph.uber.copyRecordingReferences.call(
-        this,
-        dict
-    );
-    if (c.target && dict[this.target]) {
-        c.target = (dict[this.target]);
-    }
-    return c;
-};
-
 // ColorPaletteMorph menu:
 
 ColorPaletteMorph.prototype.developersMenu = function () {
@@ -4331,7 +4320,7 @@ var GrayPaletteMorph;
 
 // GrayPaletteMorph inherits from ColorPaletteMorph:
 
-GrayPaletteMorph.prototype = new ColorPaletteMorph();
+GrayPaletteMorph.prototype = Object.create(ColorPaletteMorph.prototype);
 GrayPaletteMorph.prototype.constructor = GrayPaletteMorph;
 GrayPaletteMorph.uber = ColorPaletteMorph.prototype;
 
@@ -4362,7 +4351,7 @@ GrayPaletteMorph.prototype.drawNew = function () {
 
 // ColorPickerMorph inherits from Morph:
 
-ColorPickerMorph.prototype = new Morph();
+ColorPickerMorph.prototype = Object.create(Morph.prototype);
 ColorPickerMorph.prototype.constructor = ColorPickerMorph;
 ColorPickerMorph.uber = Morph.prototype;
 
@@ -4431,7 +4420,7 @@ var BlinkerMorph;
 
 // BlinkerMorph inherits from Morph:
 
-BlinkerMorph.prototype = new Morph();
+BlinkerMorph.prototype = Object.create(Morph.prototype);
 BlinkerMorph.prototype.constructor = BlinkerMorph;
 BlinkerMorph.uber = Morph.prototype;
 
@@ -4464,7 +4453,7 @@ var CursorMorph;
 
 // CursorMorph inherits from BlinkerMorph:
 
-CursorMorph.prototype = new BlinkerMorph();
+CursorMorph.prototype = Object.create(BlinkerMorph.prototype);
 CursorMorph.prototype.constructor = CursorMorph;
 CursorMorph.uber = BlinkerMorph.prototype;
 
@@ -4884,7 +4873,7 @@ var BoxMorph;
 
 // BoxMorph inherits from Morph:
 
-BoxMorph.prototype = new Morph();
+BoxMorph.prototype = Object.create(Morph.prototype);
 BoxMorph.prototype.constructor = BoxMorph;
 BoxMorph.uber = Morph.prototype;
 
@@ -5092,7 +5081,7 @@ var SpeechBubbleMorph;
 
 // SpeechBubbleMorph inherits from BoxMorph:
 
-SpeechBubbleMorph.prototype = new BoxMorph();
+SpeechBubbleMorph.prototype = Object.create(BoxMorph.prototype);
 SpeechBubbleMorph.prototype.constructor = SpeechBubbleMorph;
 SpeechBubbleMorph.uber = BoxMorph.prototype;
 
@@ -5392,7 +5381,7 @@ var CircleBoxMorph;
 
 // CircleBoxMorph inherits from Morph:
 
-CircleBoxMorph.prototype = new Morph();
+CircleBoxMorph.prototype = Object.create(Morph.prototype);
 CircleBoxMorph.prototype.constructor = CircleBoxMorph;
 CircleBoxMorph.uber = Morph.prototype;
 
@@ -5512,7 +5501,7 @@ var SliderButtonMorph;
 
 // SliderButtonMorph inherits from CircleBoxMorph:
 
-SliderButtonMorph.prototype = new CircleBoxMorph();
+SliderButtonMorph.prototype = Object.create(CircleBoxMorph.prototype);
 SliderButtonMorph.prototype.constructor = SliderButtonMorph;
 SliderButtonMorph.uber = CircleBoxMorph.prototype;
 
@@ -5724,7 +5713,7 @@ SliderButtonMorph.prototype.mouseMove = function () {
 
 // SliderMorph inherits from CircleBoxMorph:
 
-SliderMorph.prototype = new CircleBoxMorph();
+SliderMorph.prototype = Object.create(CircleBoxMorph.prototype);
 SliderMorph.prototype.constructor = SliderMorph;
 SliderMorph.uber = CircleBoxMorph.prototype;
 
@@ -5840,23 +5829,6 @@ SliderMorph.prototype.updateTarget = function () {
     }
 };
 
-// SliderMorph duplicating:
-
-SliderMorph.prototype.copyRecordingReferences = function (dict) {
-    // inherited, see comment in Morph
-    var c = SliderMorph.uber.copyRecordingReferences.call(
-        this,
-        dict
-    );
-    if (c.target && dict[this.target]) {
-        c.target = (dict[this.target]);
-    }
-    if (c.button && dict[this.button]) {
-        c.button = (dict[this.button]);
-    }
-    return c;
-};
-
 // SliderMorph menu:
 
 SliderMorph.prototype.developersMenu = function () {
@@ -6092,7 +6064,7 @@ var MouseSensorMorph;
 
 // MouseSensorMorph inherits from BoxMorph:
 
-MouseSensorMorph.prototype = new BoxMorph();
+MouseSensorMorph.prototype = Object.create(BoxMorph.prototype);
 MouseSensorMorph.prototype.constructor = MouseSensorMorph;
 MouseSensorMorph.uber = BoxMorph.prototype;
 
@@ -6166,7 +6138,7 @@ var TriggerMorph;
 
 // InspectorMorph inherits from BoxMorph:
 
-InspectorMorph.prototype = new BoxMorph();
+InspectorMorph.prototype = Object.create(BoxMorph.prototype);
 InspectorMorph.prototype.constructor = InspectorMorph;
 InspectorMorph.uber = BoxMorph.prototype;
 
@@ -6661,7 +6633,7 @@ var MenuItemMorph;
 
 // MenuMorph inherits from BoxMorph:
 
-MenuMorph.prototype = new BoxMorph();
+MenuMorph.prototype = Object.create(BoxMorph.prototype);
 MenuMorph.prototype.constructor = MenuMorph;
 MenuMorph.uber = BoxMorph.prototype;
 
@@ -6956,7 +6928,7 @@ MenuMorph.prototype.popUpCenteredInWorld = function (world) {
 
 // StringMorph inherits from Morph:
 
-StringMorph.prototype = new Morph();
+StringMorph.prototype = Object.create(Morph.prototype);
 StringMorph.prototype.constructor = StringMorph;
 StringMorph.uber = Morph.prototype;
 
@@ -7024,7 +6996,7 @@ StringMorph.prototype.init = function (
     this.markedBackgoundColor = new Color(60, 60, 120);
 
     // initialize inherited properties:
-    StringMorph.uber.init.call(this);
+    StringMorph.uber.init.call(this, true);
 
     // override inherited properites:
     this.color = color || new Color(0, 0, 0);
@@ -7402,6 +7374,7 @@ StringMorph.prototype.selectionStartSlot = function () {
 };
 
 StringMorph.prototype.clearSelection = function () {
+    if (!this.currentlySelecting && this.startMark === 0 && this.endMark === 0) return;
     this.currentlySelecting = false;
     this.startMark = 0;
     this.endMark = 0;
@@ -7491,7 +7464,7 @@ StringMorph.prototype.disableSelecting = function () {
 
 // TextMorph inherits from Morph:
 
-TextMorph.prototype = new Morph();
+TextMorph.prototype = Object.create(Morph.prototype);
 TextMorph.prototype.constructor = TextMorph;
 TextMorph.uber = Morph.prototype;
 
@@ -8016,7 +7989,7 @@ TextMorph.prototype.inspectIt = function () {
 
 // TriggerMorph inherits from Morph:
 
-TriggerMorph.prototype = new Morph();
+TriggerMorph.prototype = Object.create(Morph.prototype);
 TriggerMorph.prototype.constructor = TriggerMorph;
 TriggerMorph.uber = Morph.prototype;
 
@@ -8141,20 +8114,6 @@ TriggerMorph.prototype.createLabel = function () {
     this.add(this.label);
 };
 
-// TriggerMorph duplicating:
-
-TriggerMorph.prototype.copyRecordingReferences = function (dict) {
-    // inherited, see comment in Morph
-    var c = TriggerMorph.uber.copyRecordingReferences.call(
-        this,
-        dict
-    );
-    if (c.label && dict[this.label]) {
-        c.label = (dict[this.label]);
-    }
-    return c;
-};
-
 // TriggerMorph action:
 
 TriggerMorph.prototype.trigger = function () {
@@ -8285,7 +8244,7 @@ var MenuItemMorph;
 
 // MenuItemMorph inherits from TriggerMorph:
 
-MenuItemMorph.prototype = new TriggerMorph();
+MenuItemMorph.prototype = Object.create(TriggerMorph.prototype);
 MenuItemMorph.prototype.constructor = MenuItemMorph;
 MenuItemMorph.uber = TriggerMorph.prototype;
 
@@ -8444,7 +8403,7 @@ MenuItemMorph.prototype.isSelectedListItem = function () {
 
 // Frames inherit from Morph:
 
-FrameMorph.prototype = new Morph();
+FrameMorph.prototype = Object.create(Morph.prototype);
 FrameMorph.prototype.constructor = FrameMorph;
 FrameMorph.uber = Morph.prototype;
 
@@ -8500,17 +8459,6 @@ FrameMorph.prototype.fullDrawOn = function (aCanvas, aRect) {
     });
 };
 
-// FrameMorph scrolling optimization:
-
-FrameMorph.prototype.moveBy = function (delta) {
-    this.changed();
-    this.bounds = this.bounds.translateBy(delta);
-    this.children.forEach(function (child) {
-        child.silentMoveBy(delta);
-    });
-    this.changed();
-};
-
 // FrameMorph scrolling support:
 
 FrameMorph.prototype.submorphBounds = function () {
@@ -8600,20 +8548,6 @@ FrameMorph.prototype.reactToGrabOf = function () {
     this.adjustBounds();
 };
 
-// FrameMorph duplicating:
-
-FrameMorph.prototype.copyRecordingReferences = function (dict) {
-    // inherited, see comment in Morph
-    var c = FrameMorph.uber.copyRecordingReferences.call(
-        this,
-        dict
-    );
-    if (c.frame && dict[this.scrollFrame]) {
-        c.frame = (dict[this.scrollFrame]);
-    }
-    return c;
-};
-
 // FrameMorph menus:
 
 FrameMorph.prototype.developersMenu = function () {
@@ -8638,7 +8572,7 @@ FrameMorph.prototype.keepAllSubmorphsWithin = function () {
 
 // ScrollFrameMorph ////////////////////////////////////////////////////
 
-ScrollFrameMorph.prototype = new FrameMorph();
+ScrollFrameMorph.prototype = Object.create(FrameMorph.prototype);
 ScrollFrameMorph.prototype.constructor = ScrollFrameMorph;
 ScrollFrameMorph.uber = FrameMorph.prototype;
 
@@ -8958,32 +8892,23 @@ ScrollFrameMorph.prototype.mouseScroll = function (y, x) {
 
 // ScrollFrameMorph duplicating:
 
-ScrollFrameMorph.prototype.copyRecordingReferences = function (dict) {
-    // inherited, see comment in Morph
-    var c = ScrollFrameMorph.uber.copyRecordingReferences.call(
-        this,
-        dict
-    );
-    if (c.contents && dict[this.contents]) {
-        c.contents = (dict[this.contents]);
-    }
-    if (c.hBar && dict[this.hBar]) {
-        c.hBar = (dict[this.hBar]);
-        c.hBar.action = function (num) {
-            c.contents.setPosition(
-                new Point(c.left() - num, c.contents.position().y)
+ScrollFrameMorph.prototype.updateReferences = function (map) {
+    var self = this;
+    ScrollFrameMorph.uber.updateReferences.call(this, map);
+    if (this.hBar) {
+        this.hBar.action = function (num) {
+            self.contents.setPosition(
+                new Point(self.left() - num, self.contents.position().y)
             );
         };
     }
-    if (c.vBar && dict[this.vBar]) {
-        c.vBar = (dict[this.vBar]);
-        c.vBar.action = function (num) {
-            c.contents.setPosition(
-                new Point(c.contents.position().x, c.top() - num)
+    if (this.vBar) {
+        this.vBar.action = function (num) {
+            self.contents.setPosition(
+                new Point(self.contents.position().x, self.top() - num)
             );
         };
     }
-    return c;
 };
 
 // ScrollFrameMorph menu:
@@ -9013,7 +8938,7 @@ ScrollFrameMorph.prototype.toggleTextLineWrapping = function () {
 
 // ListMorph ///////////////////////////////////////////////////////////
 
-ListMorph.prototype = new ScrollFrameMorph();
+ListMorph.prototype = Object.create(ScrollFrameMorph.prototype);
 ListMorph.prototype.constructor = ListMorph;
 ListMorph.uber = ScrollFrameMorph.prototype;
 
@@ -9151,7 +9076,7 @@ ListMorph.prototype.setExtent = function (aPoint) {
 
 // StringFieldMorph inherit from FrameMorph:
 
-StringFieldMorph.prototype = new FrameMorph();
+StringFieldMorph.prototype = Object.create(FrameMorph.prototype);
 StringFieldMorph.prototype.constructor = StringFieldMorph;
 StringFieldMorph.uber = FrameMorph.prototype;
 
@@ -9243,20 +9168,6 @@ StringFieldMorph.prototype.mouseClickLeft = function (pos) {
     }
 };
 
-// StringFieldMorph duplicating:
-
-StringFieldMorph.prototype.copyRecordingReferences = function (dict) {
-    // inherited, see comment in Morph
-    var c = StringFieldMorph.uber.copyRecordingReferences.call(
-        this,
-        dict
-    );
-    if (c.text && dict[this.text]) {
-        c.text = (dict[this.text]);
-    }
-    return c;
-};
-
 // BouncerMorph ////////////////////////////////////////////////////////
 
 // I am a Demo of a stepping custom Morph
@@ -9265,7 +9176,7 @@ var BouncerMorph;
 
 // Bouncers inherit from Morph:
 
-BouncerMorph.prototype = new Morph();
+BouncerMorph.prototype = Object.create(Morph.prototype);
 BouncerMorph.prototype.constructor = BouncerMorph;
 BouncerMorph.uber = Morph.prototype;
 
@@ -9352,7 +9263,7 @@ BouncerMorph.prototype.step = function () {
 
 // HandMorph inherits from Morph:
 
-HandMorph.prototype = new Morph();
+HandMorph.prototype = Object.create(Morph.prototype);
 HandMorph.prototype.constructor = HandMorph;
 HandMorph.uber = Morph.prototype;
 
@@ -9379,7 +9290,8 @@ HandMorph.prototype.init = function (aWorld) {
     this.contextMenuEnabled = false;
 };
 
-HandMorph.prototype.changed = function () {
+HandMorph.prototype.changed =
+HandMorph.prototype.fullChanged = function () {
     var b;
     if (this.world !== null) {
         b = this.fullBounds();
@@ -9387,33 +9299,31 @@ HandMorph.prototype.changed = function () {
             this.world.broken.push(this.fullBounds().spread());
         }
     }
-
 };
 
 // HandMorph navigation:
 
-HandMorph.prototype.morphAtPointer = function () {
-    var morphs = this.world.allChildren().slice(0).reverse(),
-        myself = this,
-        result = null;
-
-    morphs.forEach(function (m) {
-        if (m.visibleBounds().containsPoint(myself.bounds.origin) &&
-                result === null &&
-                m.isVisible &&
-                (m.noticesTransparentClick ||
-                    (!m.isTransparentAt(myself.bounds.origin))) &&
-                (!(m instanceof ShadowMorph)) &&
-                m.allParents().every(function (each) {
-                    return each.isVisible;
-                })) {
-            result = m;
-        }
-    });
-    if (result !== null) {
-        return result;
+Morph.prototype.topMorphAt = function (p) {
+    if (!this.isVisible) return null;
+    for (var c = this.children, i = c.length; i--;) {
+        var result = c[i].topMorphAt(p);
+        if (result) return result;
+    }
+    return this.bounds.containsPoint(p) && (this.noticesTransparentClick || !this.isTransparentAt(p)) ? this : null;
+};
+FrameMorph.prototype.topMorphAt = function (p) {
+    if (!(this.isVisible && this.bounds.containsPoint(p))) return null;
+    for (var c = this.children, i = c.length; i--;) {
+        var result = c[i].topMorphAt(p);
+        if (result) return result;
     }
-    return this.world;
+    return this.noticesTransparentClick || !this.isTransparentAt(p) ? this : null;
+};
+ShadowMorph.prototype.topMorphAt = function () {
+    return null;
+};
+HandMorph.prototype.morphAtPointer = function () {
+    return this.world.topMorphAt(this.bounds.origin) || this.world;
 };
 
 /*
@@ -9971,15 +9881,6 @@ HandMorph.prototype.destroyTemporaries = function () {
     });
 };
 
-// HandMorph dragging optimization
-
-HandMorph.prototype.moveBy = function (delta) {
-    Morph.prototype.trackChanges = false;
-    HandMorph.uber.moveBy.call(this, delta);
-    Morph.prototype.trackChanges = true;
-    this.fullChanged();
-};
-
 
 // WorldMorph //////////////////////////////////////////////////////////
 
@@ -9987,7 +9888,7 @@ HandMorph.prototype.moveBy = function (delta) {
 
 // WorldMorph inherits from FrameMorph:
 
-WorldMorph.prototype = new FrameMorph();
+WorldMorph.prototype = Object.create(FrameMorph.prototype);
 WorldMorph.prototype.constructor = WorldMorph;
 WorldMorph.uber = FrameMorph.prototype;
 
@@ -10009,6 +9910,7 @@ WorldMorph.prototype.init = function (aCanvas, fillPage) {
     this.isDraggable = false;
     this.currentKey = null; // currently pressed key code
     this.worldCanvas = aCanvas;
+    this.noticesTransparentClick = true;
 
     // additional properties:
     this.stamp = Date.now(); // reference in multi-world setups
diff --git a/objects.js b/objects.js
index 8cae1c7..1e8060e 100644
--- a/objects.js
+++ b/objects.js
@@ -105,7 +105,7 @@ InspectorMorph, ListMorph, Math, MenuItemMorph, MenuMorph, Morph,
 MorphicPreferences, MouseSensorMorph, Node, Object, PenMorph, Point,
 Rectangle, ScrollFrameMorph, ShadowMorph, SliderButtonMorph,
 SliderMorph, String, StringFieldMorph, StringMorph, TextMorph,
-TriggerMorph, WorldMorph, clone, contains, copy, degrees, detect,
+TriggerMorph, WorldMorph, contains, copy, degrees, detect,
 document, getDocumentPositionOf, isNaN, isObject, isString, newCanvas,
 nop, parseFloat, radians, standardSettings, touchScreenSettings,
 useBlurredShadows, version, window, modules, IDE_Morph, VariableDialogMorph,
@@ -147,7 +147,7 @@ var SpriteHighlightMorph;
 
 // SpriteMorph inherits from PenMorph:
 
-SpriteMorph.prototype = new PenMorph();
+SpriteMorph.prototype = Object.create(PenMorph.prototype);
 SpriteMorph.prototype.constructor = SpriteMorph;
 SpriteMorph.uber = PenMorph.prototype;
 
@@ -583,7 +583,7 @@ SpriteMorph.prototype.initBlocks = function () {
         },
 
     /* migrated to a newer block version:
-  
+
         receiveClick: {
             type: 'hat',
             category: 'control',
@@ -3008,7 +3008,7 @@ SpriteMorph.prototype.applyGraphicsEffects = function (canvas) {
         var i;
         if (value !== 0) {
             for (i = 0; i < p.length; i += 4) {
-                p[i] += value; //255 = 100% of this color 
+                p[i] += value; //255 = 100% of this color
                 p[i + 1] += value;
                 p[i + 2] += value;
             }
@@ -3290,7 +3290,7 @@ SpriteMorph.prototype.nestingBounds = function () {
 
 // SpriteMorph motion primitives
 
-Morph.prototype.setPosition = function (aPoint, justMe) {
+SpriteMorph.prototype.setPosition = function (aPoint, justMe) {
     // override the inherited default to make sure my parts follow
     // unless it's justMe
     var delta = aPoint.subtract(this.topLeft());
@@ -4289,7 +4289,7 @@ SpriteMorph.prototype.doScreenshot = function (imgSource, data) {
 
 // SpriteHighlightMorph inherits from Morph:
 
-SpriteHighlightMorph.prototype = new Morph();
+SpriteHighlightMorph.prototype = Object.create(Morph.prototype);
 SpriteHighlightMorph.prototype.constructor = SpriteHighlightMorph;
 SpriteHighlightMorph.uber = Morph.prototype;
 
@@ -4307,7 +4307,7 @@ function SpriteHighlightMorph() {
 
 // StageMorph inherits from FrameMorph:
 
-StageMorph.prototype = new FrameMorph();
+StageMorph.prototype = Object.create(FrameMorph.prototype);
 StageMorph.prototype.constructor = StageMorph;
 StageMorph.uber = FrameMorph.prototype;
 
@@ -5669,7 +5669,7 @@ StageMorph.prototype.replaceDoubleDefinitionsFor
 
 // SpriteBubbleMorph inherits from SpeechBubbleMorph:
 
-SpriteBubbleMorph.prototype = new SpeechBubbleMorph();
+SpriteBubbleMorph.prototype = Object.create(SpeechBubbleMorph.prototype);
 SpriteBubbleMorph.prototype.constructor = SpriteBubbleMorph;
 SpriteBubbleMorph.uber = SpeechBubbleMorph.prototype;
 
@@ -6168,7 +6168,7 @@ Costume.prototype.isTainted = function () {
 
 // SVG_Costume inherits from Costume:
 
-SVG_Costume.prototype = new Costume();
+SVG_Costume.prototype = Object.create(Costume.prototype);
 SVG_Costume.prototype.constructor = SVG_Costume;
 SVG_Costume.uber = Costume.prototype;
 
@@ -6219,7 +6219,7 @@ SVG_Costume.prototype.shrinkToFit = function (extentPoint) {
 
 // CostumeEditorMorph inherits from Morph:
 
-CostumeEditorMorph.prototype = new Morph();
+CostumeEditorMorph.prototype = Object.create(Morph.prototype);
 CostumeEditorMorph.prototype.constructor = CostumeEditorMorph;
 CostumeEditorMorph.uber = Morph.prototype;
 
@@ -6454,7 +6454,7 @@ Note.prototype.stop = function () {
 
 // CellMorph inherits from BoxMorph:
 
-CellMorph.prototype = new BoxMorph();
+CellMorph.prototype = Object.create(BoxMorph.prototype);
 CellMorph.prototype.constructor = CellMorph;
 CellMorph.uber = BoxMorph.prototype;
 
@@ -6794,7 +6794,7 @@ CellMorph.prototype.mouseClickLeft = function (pos) {
 
 // WatcherMorph inherits from BoxMorph:
 
-WatcherMorph.prototype = new BoxMorph();
+WatcherMorph.prototype = Object.create(BoxMorph.prototype);
 WatcherMorph.prototype.constructor = WatcherMorph;
 WatcherMorph.uber = BoxMorph.prototype;
 
@@ -7281,7 +7281,7 @@ WatcherMorph.prototype.drawNew = function () {
 
 // StagePrompterMorph inherits from BoxMorph:
 
-StagePrompterMorph.prototype = new BoxMorph();
+StagePrompterMorph.prototype = Object.create(BoxMorph.prototype);
 StagePrompterMorph.prototype.constructor = StagePrompterMorph;
 StagePrompterMorph.uber = BoxMorph.prototype;
 
diff --git a/paint.js b/paint.js
index 65ae1f6..6e4ae8b 100644
--- a/paint.js
+++ b/paint.js
@@ -81,7 +81,7 @@ var PaintColorPickerMorph;
 
 // A complete paint editor
 
-PaintEditorMorph.prototype = new DialogBoxMorph();
+PaintEditorMorph.prototype = Object.create(DialogBoxMorph.prototype);
 PaintEditorMorph.prototype.constructor = PaintEditorMorph;
 PaintEditorMorph.uber = DialogBoxMorph.prototype;
 
@@ -92,6 +92,7 @@ function PaintEditorMorph() {
 }
 
 PaintEditorMorph.prototype.init = function () {
+    PaintEditorMorph.uber.init.call(this);
     // additional properties:
     this.paper = null; // paint canvas
     this.oncancel = null;
@@ -476,7 +477,7 @@ PaintEditorMorph.prototype.getUserColor = function () {
 
 // A large hsl color picker
 
-PaintColorPickerMorph.prototype = new Morph();
+PaintColorPickerMorph.prototype = Object.create(Morph.prototype);
 PaintColorPickerMorph.prototype.constructor = PaintColorPickerMorph;
 PaintColorPickerMorph.uber = Morph.prototype;
 
@@ -485,6 +486,7 @@ function PaintColorPickerMorph(extent, action) {
 }
 
 PaintColorPickerMorph.prototype.init = function (extent, action) {
+    PaintColorPickerMorph.uber.init.call(this);
     this.setExtent(extent || new Point(200, 100));
     this.action = action || nop;
     this.drawNew();
@@ -552,7 +554,7 @@ PaintColorPickerMorph.prototype.mouseMove =
     modify its image, based on a 'tool' property.
 */
 
-PaintCanvasMorph.prototype = new Morph();
+PaintCanvasMorph.prototype = Object.create(Morph.prototype);
 PaintCanvasMorph.prototype.constructor = PaintCanvasMorph;
 PaintCanvasMorph.uber = Morph.prototype;
 
@@ -561,6 +563,7 @@ function PaintCanvasMorph(shift) {
 }
 
 PaintCanvasMorph.prototype.init = function (shift) {
+    PaintCanvasMorph.uber.init.call(this);
     this.rotationCenter = new Point(240, 180);
     this.dragRect = null;
     this.previousDragPoint = null;
@@ -961,6 +964,7 @@ PaintCanvasMorph.prototype.buildContents = function () {
 };
 
 PaintCanvasMorph.prototype.drawNew = function () {
+    if (!this.background) return;
     var can = newCanvas(this.extent());
     this.merge(this.background, can);
     this.merge(this.paper, can);
diff --git a/store.js b/store.js
index 5cba3c3..a45c801 100644
--- a/store.js
+++ b/store.js
@@ -246,7 +246,7 @@ var SnapSerializer;
 
 // SnapSerializer inherits from XML_Serializer:
 
-SnapSerializer.prototype = new XML_Serializer();
+SnapSerializer.prototype = Object.create(XML_Serializer.prototype);
 SnapSerializer.prototype.constructor = SnapSerializer;
 SnapSerializer.uber = XML_Serializer.prototype;
 
@@ -274,6 +274,7 @@ SnapSerializer.prototype.watcherLabels = {
 // SnapSerializer instance creation:
 
 function SnapSerializer() {
+    XML_Serializer.call(this);
     this.init();
 }
 
diff --git a/widgets.js b/widgets.js
index bb250a8..2f96f2c 100644
--- a/widgets.js
+++ b/widgets.js
@@ -91,7 +91,7 @@ var InputFieldMorph;
 
 // PushButtonMorph inherits from TriggerMorph:
 
-PushButtonMorph.prototype = new TriggerMorph();
+PushButtonMorph.prototype = Object.create(TriggerMorph.prototype);
 PushButtonMorph.prototype.constructor = PushButtonMorph;
 PushButtonMorph.uber = TriggerMorph.prototype;
 
@@ -476,7 +476,7 @@ PushButtonMorph.prototype.createLabel = function () {
 
 // ToggleButtonMorph inherits from PushButtonMorph:
 
-ToggleButtonMorph.prototype = new PushButtonMorph();
+ToggleButtonMorph.prototype = Object.create(PushButtonMorph.prototype);
 ToggleButtonMorph.prototype.constructor = ToggleButtonMorph;
 ToggleButtonMorph.uber = PushButtonMorph.prototype;
 
@@ -900,7 +900,7 @@ ToggleButtonMorph.prototype.show = function () {
 
 // TabMorph inherits from ToggleButtonMorph:
 
-TabMorph.prototype = new ToggleButtonMorph();
+TabMorph.prototype = Object.create(ToggleButtonMorph.prototype);
 TabMorph.prototype.constructor = TabMorph;
 TabMorph.uber = ToggleButtonMorph.prototype;
 
@@ -1022,7 +1022,7 @@ TabMorph.prototype.drawEdges = function (
 
 // ToggleMorph inherits from PushButtonMorph:
 
-ToggleMorph.prototype = new PushButtonMorph();
+ToggleMorph.prototype = Object.create(PushButtonMorph.prototype);
 ToggleMorph.prototype.constructor = ToggleMorph;
 ToggleMorph.uber = PushButtonMorph.prototype;
 
@@ -1270,7 +1270,7 @@ ToggleMorph.prototype.show = ToggleButtonMorph.prototype.show;
 
 // ToggleElementMorph inherits from TriggerMorph:
 
-ToggleElementMorph.prototype = new TriggerMorph();
+ToggleElementMorph.prototype = Object.create(TriggerMorph.prototype);
 ToggleElementMorph.prototype.constructor = ToggleElementMorph;
 ToggleElementMorph.uber = TriggerMorph.prototype;
 
@@ -1440,7 +1440,7 @@ ToggleElementMorph.prototype.mouseClickLeft
 
 // DialogBoxMorph inherits from Morph:
 
-DialogBoxMorph.prototype = new Morph();
+DialogBoxMorph.prototype = Object.create(Morph.prototype);
 DialogBoxMorph.prototype.constructor = DialogBoxMorph;
 DialogBoxMorph.uber = Morph.prototype;
 
@@ -2866,7 +2866,7 @@ DialogBoxMorph.prototype.outlinePathBody = function (context, radius) {
 
 // AlignmentMorph inherits from Morph:
 
-AlignmentMorph.prototype = new Morph();
+AlignmentMorph.prototype = Object.create(Morph.prototype);
 AlignmentMorph.prototype.constructor = AlignmentMorph;
 AlignmentMorph.uber = Morph.prototype;
 
@@ -2940,7 +2940,7 @@ AlignmentMorph.prototype.fixLayout = function () {
 
 // InputFieldMorph inherits from Morph:
 
-InputFieldMorph.prototype = new Morph();
+InputFieldMorph.prototype = Object.create(Morph.prototype);
 InputFieldMorph.prototype.constructor = InputFieldMorph;
 InputFieldMorph.uber = Morph.prototype;
 
diff --git a/xml.js b/xml.js
index fb612ce..16b03f0 100644
--- a/xml.js
+++ b/xml.js
@@ -61,7 +61,7 @@
 
 */
 
-/*global modules, isString, detect, Node, isNil*/
+/*global modules, detect, Node, isNil*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
@@ -85,7 +85,8 @@ function ReadStream(arrayOrString) {
 
 // ReadStream constants:
 
-ReadStream.prototype.space = /[\s]/;
+ReadStream.prototype.nonSpace = /\S|$/g;
+ReadStream.prototype.nonWord = /[\s\>\/\=]|$/g;
 
 // ReadStream accessing:
 
@@ -115,46 +116,26 @@ ReadStream.prototype.atEnd = function () {
 
 // ReadStream accessing String contents:
 
-ReadStream.prototype.upTo = function (regex) {
-    var i, start;
-    if (!isString(this.contents)) {return ''; }
-    i = this.contents.substr(this.index).search(regex);
-    if (i === -1) {
-        return '';
-    }
-    start = this.index;
-    this.index += i;
-    return this.contents.substring(start, this.index);
+ReadStream.prototype.upTo = function (str) {
+    var i = this.contents.indexOf(str, this.index);
+    return i === -1 ? '' : this.contents.slice(this.index, this.index = i);
 };
 
-ReadStream.prototype.peekUpTo = function (regex) {
-    if (!isString(this.contents)) {return ''; }
-    var i = this.contents.substr(this.index).search(regex);
-    if (i === -1) {
-        return '';
-    }
-    return this.contents.substring(this.index, this.index + i);
+ReadStream.prototype.peekUpTo = function (str) {
+    var i = this.contents.indexOf(str, this.index);
+    return i === -1 ? '' : this.contents.slice(this.index, i);
 };
 
 ReadStream.prototype.skipSpace = function () {
-    if (!isString(this.contents)) {return ''; }
-    var ch = this.peek();
-    while (this.space.test(ch) && ch !== '') {
-        this.skip();
-        ch = this.peek();
-    }
+    this.nonSpace.lastIndex = this.index;
+    var result = this.nonSpace.exec(this.contents);
+    if (result) this.index = result.index;
 };
 
 ReadStream.prototype.word = function () {
-    var i, start;
-    if (!isString(this.contents)) {return ''; }
-    i = this.contents.substr(this.index).search(/[\s\>\/\=]|$/);
-    if (i === -1) {
-        return '';
-    }
-    start = this.index;
-    this.index += i;
-    return this.contents.substring(start, this.index);
+    this.nonWord.lastIndex = this.index;
+    var result = this.nonWord.exec(this.contents);
+    return result ? this.contents.slice(this.index, this.index = result.index) : '';
 };
 
 // XML_Element ///////////////////////////////////////////////////////////
@@ -166,7 +147,7 @@ ReadStream.prototype.word = function () {
 
 // XML_Element inherits from Node:
 
-XML_Element.prototype = new Node();
+XML_Element.prototype = Object.create(Node.prototype);
 XML_Element.prototype.constructor = XML_Element;
 XML_Element.uber = Node.prototype;
 
@@ -190,9 +171,7 @@ XML_Element.prototype.init = function (tag, contents, parent) {
     XML_Element.uber.init.call(this);
 
     // override inherited properties
-    if (parent instanceof XML_Element) {
-        parent.addChild(this);
-    }
+    if (parent) parent.addChild(this);
 };
 
 // XML_Element DOM navigation: (aside from what's inherited from Node)
@@ -318,51 +297,18 @@ XML_Element.prototype.escape = function (string, ignoreQuotes) {
 };
 
 XML_Element.prototype.unescape = function (string) {
-    var stream = new ReadStream(string),
-        result = '',
-        ch,
-        esc;
-
-    function nextPut(str) {
-        result += str;
-        stream.upTo(';');
-        stream.skip();
-    }
-
-    while (!stream.atEnd()) {
-        ch = stream.next();
-        if (ch === '&') {
-            esc = stream.peekUpTo(';');
-            switch (esc) {
-            case 'apos':
-                nextPut('\'');
-                break;
-            case 'quot':
-                nextPut('\"');
-                break;
-            case 'lt':
-                nextPut('<');
-                break;
-            case 'gt':
-                nextPut('>');
-                break;
-            case 'amp':
-                nextPut('&');
-                break;
-            case '#xD':
-                nextPut('\n');
-                break;
-            case '#126':
-                nextPut('~');
-                break;
-            default:
-                result += ch;
-            }
-        } else {
-            result += ch;
+    return string.replace(/&(amp|apos|quot|lt|gt|#xD|#126);/g, function(_, name) {
+        switch (name) {
+            case 'amp': return '&';
+            case 'apos': return '\'';
+            case 'quot': return '"';
+            case 'lt': return '<';
+            case 'gt': return '>';
+            case '#xD': return '\n';
+            case '#126': return '~';
+            default: console.warn('unreachable');
         }
-    }
-    return result;
+    });
 };
 
 // XML_Element parsing:
@@ -375,10 +321,7 @@ XML_Element.prototype.parseString = function (string) {
 };
 
 XML_Element.prototype.parseStream = function (stream) {
-    var key,
-        value,
-        ch,
-        child;
+    var key, value, ch, child;
 
     // tag:
     this.tag = stream.word();
@@ -395,9 +338,7 @@ XML_Element.prototype.parseStream = function (stream) {
         stream.skipSpace();
         ch = stream.next();
         if (ch !== '"' && ch !== "'") {
-            throw new Error(
-                'Expected single- or double-quoted attribute value'
-            );
+            throw new Error('Expected single- or double-quoted attribute value');
         }
         value = stream.upTo(ch);
         stream.skip(1);
@@ -407,7 +348,7 @@ XML_Element.prototype.parseStream = function (stream) {
     }
 
     // empty tag:
-    if (stream.peek() === '/') {
+    if (ch === '/') {
         stream.skip();
         if (stream.next() !== '>') {
             throw new Error('Expected ">" after "/" in empty tag');