diff --git a/lib/carto/renderer.js b/lib/carto/renderer.js
index 6af4be7..cd17d72 100644
--- a/lib/carto/renderer.js
+++ b/lib/carto/renderer.js
@@ -172,8 +172,8 @@ function addRules(current, definition, existing) {
                     k++;
                 }
             }
-        } else if (updatedFilters === null &&
-            current[k].zoom === definition.zoom) {
+        } else if (updatedFilters === null) { // &&
+            // current[k].zoom === definition.zoom) {
             // Filters can be added, but they don't change the
             // filters. This means we don't have to split the
             // definition.
diff --git a/lib/carto/tree/call.js b/lib/carto/tree/call.js
index 8ba29d6..fcefd28 100644
--- a/lib/carto/tree/call.js
+++ b/lib/carto/tree/call.js
@@ -2,14 +2,13 @@
 var _ = require('underscore');
 
 tree.Call = function Call(name, args, index) {
-    this.is = 'call';
-
     this.name = name;
     this.args = args;
     this.index = index;
 };
 
 tree.Call.prototype = {
+    is: 'call',
     //
     // When evaluating a function call,
     // we either find the function in `tree.functions` [1],
diff --git a/lib/carto/tree/color.js b/lib/carto/tree/color.js
index 213b2bc..24b94de 100644
--- a/lib/carto/tree/color.js
+++ b/lib/carto/tree/color.js
@@ -20,11 +20,11 @@ tree.Color = function Color(rgb, a) {
             return parseInt(c + c, 16);
         });
     }
-    this.is = 'color';
     this.alpha = typeof(a) === 'number' ? a : 1;
 };
 
 tree.Color.prototype = {
+    is: 'color',
     eval: function() { return this; },
 
     // If we have some transparency, the only way to represent it
diff --git a/lib/carto/tree/definition.js b/lib/carto/tree/definition.js
index 446d678..9b6f2db 100644
--- a/lib/carto/tree/definition.js
+++ b/lib/carto/tree/definition.js
@@ -1,6 +1,12 @@
 (function(tree) {
 var assert = require('assert');
 
+// A definition is the combination of a selector and rules, like
+// #foo {
+//     polygon-opacity:1.0;
+// }
+//
+// The selector can have filters
 tree.Definition = function Definition(selector, rules) {
     this.elements = selector.elements;
     assert.ok(selector.filters instanceof tree.Filterset);
@@ -50,11 +56,9 @@ tree.Definition.prototype.addRules = function(rules) {
     return added;
 };
 
-/**
- * Determine whether this selector matches a given id
- * and array of classes, by determining whether
- * all elements it contains match.
- */
+// Determine whether this selector matches a given id
+// and array of classes, by determining whether
+// all elements it contains match.
 tree.Definition.prototype.appliesTo = function(id, classes) {
     for (var i = 0; i < this.elements.length; i++) {
         if (!this.elements[i].matches(id, classes)) {
diff --git a/lib/carto/tree/dimension.js b/lib/carto/tree/dimension.js
index cfd3621..4d061da 100644
--- a/lib/carto/tree/dimension.js
+++ b/lib/carto/tree/dimension.js
@@ -6,11 +6,11 @@
 tree.Dimension = function Dimension(value, unit, index) {
     this.value = parseFloat(value);
     this.unit = unit || null;
-    this.is = 'float';
     this.index = index;
 };
 
 tree.Dimension.prototype = {
+    is: 'float',
     eval: function (env) {
         if (this.unit && ['px', '%'].indexOf(this.unit) === -1) {
              env.error({
diff --git a/lib/carto/tree/expression.js b/lib/carto/tree/expression.js
index 1bf7108..b02fd63 100644
--- a/lib/carto/tree/expression.js
+++ b/lib/carto/tree/expression.js
@@ -2,10 +2,10 @@
 
 tree.Expression = function Expression(value) {
     this.value = value;
-    this.is = 'expression';
 };
 
 tree.Expression.prototype = {
+    is: 'expression',
     eval: function(env) {
         if (this.value.length > 1) {
             return new tree.Expression(this.value.map(function(e) {
diff --git a/lib/carto/tree/field.js b/lib/carto/tree/field.js
index f6ebe8d..645cc60 100644
--- a/lib/carto/tree/field.js
+++ b/lib/carto/tree/field.js
@@ -2,10 +2,10 @@
 
 tree.Field = function Field(content) {
     this.value = content || '';
-    this.is = 'field';
 };
 
 tree.Field.prototype = {
+    is: 'field',
     toString: function() {
         return '[' + this.value + ']';
     },
diff --git a/lib/carto/tree/imagefilter.js b/lib/carto/tree/imagefilter.js
index 9fcd2cc..6adfe0b 100644
--- a/lib/carto/tree/imagefilter.js
+++ b/lib/carto/tree/imagefilter.js
@@ -1,13 +1,10 @@
 (function(tree) {
-//
-// RGB Colors - #ff0014, #eee
-//
 tree.ImageFilter = function ImageFilter(filter, args) {
-    this.is = 'imagefilter';
     this.filter = filter;
     this.args = args || null;
 };
 tree.ImageFilter.prototype = {
+    is: 'imagefilter',
     eval: function() { return this; },
 
     toString: function() {
diff --git a/lib/carto/tree/invalid.js b/lib/carto/tree/invalid.js
index 70ace6d..cdc90c3 100644
--- a/lib/carto/tree/invalid.js
+++ b/lib/carto/tree/invalid.js
@@ -4,9 +4,10 @@ tree.Invalid = function Invalid(chunk, index, message) {
     this.index = index;
     this.type = 'syntax';
     this.message = message || "Invalid code: " + this.chunk;
-    this.is = 'invalid';
 };
 
+tree.Invalid.prototype.is = 'invalid';
+
 tree.Invalid.prototype.eval = function(env) {
     env.error({
         chunk: this.chunk,
diff --git a/lib/carto/tree/operation.js b/lib/carto/tree/operation.js
index 627063a..95a1822 100644
--- a/lib/carto/tree/operation.js
+++ b/lib/carto/tree/operation.js
@@ -1,12 +1,15 @@
+// An operation is an expression with an op in between two operands,
+// like 2 + 1.
 (function(tree) {
 
 tree.Operation = function Operation(op, operands, index) {
     this.op = op.trim();
     this.operands = operands;
     this.index = index;
-    this.is = 'operation';
 };
 
+tree.Operation.prototype.is = 'operation';
+
 tree.Operation.prototype.eval = function(env) {
     var a = this.operands[0].eval(env),
         b = this.operands[1].eval(env),
diff --git a/lib/carto/tree/quoted.js b/lib/carto/tree/quoted.js
index 51dddb5..180822b 100644
--- a/lib/carto/tree/quoted.js
+++ b/lib/carto/tree/quoted.js
@@ -2,10 +2,11 @@
 
 tree.Quoted = function Quoted(content) {
     this.value = content || '';
-    this.is = 'string';
 };
 
 tree.Quoted.prototype = {
+    is: 'string',
+
     toString: function(quotes) {
         var xmlvalue = this.value.replace(/\'/g, '&apos;');
         return (quotes === true) ? "'" + xmlvalue + "'" : this.value;
diff --git a/lib/carto/tree/reference.js b/lib/carto/tree/reference.js
index 8db1777..2f76bc5 100644
--- a/lib/carto/tree/reference.js
+++ b/lib/carto/tree/reference.js
@@ -1,9 +1,7 @@
-/*
- * Carto pulls in a reference from the `mapnik-reference`
- * module. This file builds indexes from that file for its various
- * options, and provides validation methods for property: value
- * combinations.
- */
+// Carto pulls in a reference from the `mapnik-reference`
+// module. This file builds indexes from that file for its various
+// options, and provides validation methods for property: value
+// combinations.
 (function(tree) {
 
 var _ = require('underscore');
@@ -72,10 +70,8 @@ tree.Reference.symbolizer = function(selector) {
     }
 };
 
-/*
- * For transform properties and image-filters,
- * mapnik has its own functions.
- */
+// For transform properties and image-filters,
+// mapnik has its own functions.
 tree.Reference.mapnikFunctions = function() {
     var functions = [];
     for (var i in tree.Reference.data.symbolizers) {
@@ -88,10 +84,8 @@ tree.Reference.mapnikFunctions = function() {
     return functions;
 };
 
-/*
- * For transform properties and image-filters,
- * mapnik has its own functions.
- */
+// For transform properties and image-filters,
+// mapnik has its own functions.
 tree.Reference.mapnikFunction = function(name) {
     return _.find(this.mapnikFunctions(), function(f) {
         return f[0] === name;
diff --git a/lib/carto/tree/rule.js b/lib/carto/tree/rule.js
index 6f50e61..5fd25f6 100644
--- a/lib/carto/tree/rule.js
+++ b/lib/carto/tree/rule.js
@@ -1,4 +1,7 @@
 (function(tree) {
+// a rule is a single property and value combination, or variable
+// name and value combination, like
+// polygon-opacity: 1.0; or @opacity: 1.0;
 tree.Rule = function Rule(name, value, index, filename) {
     var parts = name.split('/');
     this.name = parts.pop();
@@ -105,9 +108,7 @@ tree.Rule.prototype.toXML = function(env, content, sep, format) {
     }
 };
 
-/**
- * TODO: Rule eval chain should add fontsets to env.frames
- */
+// TODO: Rule eval chain should add fontsets to env.frames
 tree.Rule.prototype['eval'] = function(context) {
     return new tree.Rule(this.name,
         this.value['eval'](context),
diff --git a/lib/carto/tree/ruleset.js b/lib/carto/tree/ruleset.js
index 2bc6d4a..f1b00a4 100644
--- a/lib/carto/tree/ruleset.js
+++ b/lib/carto/tree/ruleset.js
@@ -8,6 +8,7 @@ tree.Ruleset = function Ruleset(selectors, rules) {
     this.is = 'ruleset';
 };
 tree.Ruleset.prototype = {
+    is: 'ruleset',
     'eval': function(env) {
         var i,
             ruleset = new tree.Ruleset(this.selectors, this.rules.slice(0));
diff --git a/package.json b/package.json
index 7cbcf19..4f5fe67 100644
--- a/package.json
+++ b/package.json
@@ -3,10 +3,12 @@
   "version": "0.9.4",
   "description": "Mapnik Stylesheet Compiler",
   "url": "https://github.com/mapbox/carto",
-  "repositories": [{
-    "type": "git",
-    "url": "http://github.com/mapbox/carto.git"
-  }],
+  "repositories": [
+    {
+      "type": "git",
+      "url": "http://github.com/mapbox/carto.git"
+    }
+  ],
   "author": {
     "name": "MapBox",
     "url": "http://mapbox.com/",
@@ -23,9 +25,11 @@
     "Konstantin Käfer",
     "Alexis Sellier <self@cloudhead.net>"
   ],
-  "licenses": [{
-    "type": "Apache"
-  }],
+  "licenses": [
+    {
+      "type": "Apache"
+    }
+  ],
   "bin": {
     "carto": "./bin/carto",
     "mml2json.js": "./bin/mml2json.js"
@@ -37,7 +41,8 @@
   "dependencies": {
     "underscore": "~1.3.3",
     "mapnik-reference": "~5.0.0",
-    "xml2js": "~0.1.13"
+    "xml2js": "~0.1.13",
+    "lodash": "~1.0.0-rc.3"
   },
   "devDependencies": {
     "mocha": "1.3.x",
diff --git a/test/quoted.test.js b/test/quoted.test.js
new file mode 100644
index 0000000..10c6b67
--- /dev/null
+++ b/test/quoted.test.js
@@ -0,0 +1,23 @@
+var assert = require('assert');
+var tree = require('../lib/carto/tree.js');
+require('../lib/carto/tree/quoted');
+
+describe('Quoted', function() {
+    describe('basic functionality', function() {
+        it('should be constructed', function() {
+            var f = new tree.Quoted("Tom's quoted");
+            assert.ok(f);
+            assert.equal(f.is, 'string');
+        });
+        it('should produce normal output', function() {
+            var f = new tree.Quoted("Tom's quoted");
+            assert.ok(f);
+            assert.equal(f.toString(), "Tom's quoted");
+        });
+        it('should produce xml-friendly output', function() {
+            var f = new tree.Quoted("Tom's quoted");
+            assert.ok(f);
+            assert.equal(f.toString(true), "'Tom&apos;s quoted'");
+        });
+    });
+});