diff --git a/lib/carto/parser.js b/lib/carto/parser.js
index 13ef3bc..82a47fd 100644
--- a/lib/carto/parser.js
+++ b/lib/carto/parser.js
@@ -806,7 +806,7 @@ carto.Parser = function Parser(env) {
                 if (! $('[')) return;
                 if (key = $(/^[a-zA-Z0-9-_]+/) || $(this.entities.quoted)) {
                     if ((op = $(this.entities.comparison)) &&
-                        (val = $(this.entities.quoted) || $(/^[\w-\.]+/))) {
+                        (val = $(this.entities.quoted) || $(this.entities.variable) || $(/^[\w-\.]+/))) {
                         if (! $(']')) return;
                         return new tree.Filter(key, op, val, memo);
                     }
diff --git a/lib/carto/tree/filter.js b/lib/carto/tree/filter.js
index 6ee29b8..bc9257a 100644
--- a/lib/carto/tree/filter.js
+++ b/lib/carto/tree/filter.js
@@ -41,6 +41,7 @@ var opXML = {
 };
 
 tree.Filter.prototype.toXML = function(env) {
+    if (this.val.eval) this._val = this.val.eval(env);
     if (this._key) var key = this._key.toString(this._key.is == 'string');
     if (this._val) var val = this._val.toString(this._val.is == 'string');
 
diff --git a/lib/carto/tree/layer.js b/lib/carto/tree/layer.js
index 6a6c532..3689140 100644
--- a/lib/carto/tree/layer.js
+++ b/lib/carto/tree/layer.js
@@ -10,8 +10,8 @@ tree.Layer = function Layer(obj) {
 tree.Layer.prototype.toXML = function() {
     var dsoptions = [];
     for (var i in this.datasource) {
-        dsoptions.push('<Parameter name="' + i + '">' +
-            this.datasource[i] + '</Parameter>');
+        dsoptions.push('<Parameter name="' + i + '"><![CDATA[' +
+            this.datasource[i] + ']]></Parameter>');
     }
     return '<Layer\n   ' +
         '   name="' + this.name + '"\n' +
diff --git a/test/rendering.test.js b/test/rendering.test.js
index 3182e0d..7b96dcf 100644
--- a/test/rendering.test.js
+++ b/test/rendering.test.js
@@ -38,7 +38,7 @@ helper.files('rendering', 'mml', function(file) {
                             helper.showDifferences(err);
                             throw '';
                         }
-                    }, [ 
+                    }, [
                         helper.removeAbsoluteImages,
                         helper.removeAbsoluteDatasources
                     ]);
diff --git a/test/rendering/zoomlevels.result b/test/rendering/zoomlevels.result
index deac9e8..5ca98c1 100644
--- a/test/rendering/zoomlevels.result
+++ b/test/rendering/zoomlevels.result
@@ -1,89 +1,102 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!DOCTYPE Map[]>
-<Map  srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs">
+<Map srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over">
 
 
 <Style name="world" filter-mode="first">
   <Rule>
     <MinScaleDenominator>50000000</MinScaleDenominator>
-    <PolygonSymbolizer fill="#ffff00"/>
+    <PolygonSymbolizer fill="#ffff00" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>1500000</MaxScaleDenominator><MinScaleDenominator>750000</MinScaleDenominator>
-    <PolygonSymbolizer fill="#000000"/>
+    <MaxScaleDenominator>1500000</MaxScaleDenominator>
+    <MinScaleDenominator>750000</MinScaleDenominator>
+    <PolygonSymbolizer fill="#000000" />
   </Rule>
 </Style>
 <Layer
-   name="world"
-   srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs">
+      name="world"
+   srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over">
     <StyleName>world</StyleName>
     <Datasource>
-       <Parameter name="file">[absolute path]</Parameter>
-       <Parameter name="type">shape</Parameter>
+       <Parameter name="file"><![CDATA[[absolute path]]]></Parameter>
+       <Parameter name="type"><![CDATA[shape]]></Parameter>
     </Datasource>
   </Layer>
 
 <Style name="countries" filter-mode="first">
   <Rule>
     <MaxScaleDenominator>100000</MaxScaleDenominator>
-    <LineSymbolizer stroke-width="0.25"/>
+    <LineSymbolizer stroke-width="0.25" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>200000</MaxScaleDenominator><MinScaleDenominator>100000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="0.3"/>
+    <MaxScaleDenominator>200000</MaxScaleDenominator>
+    <MinScaleDenominator>100000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="0.3" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>400000</MaxScaleDenominator><MinScaleDenominator>200000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="0.4"/>
+    <MaxScaleDenominator>400000</MaxScaleDenominator>
+    <MinScaleDenominator>200000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="0.4" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>750000</MaxScaleDenominator><MinScaleDenominator>400000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="0.5"/>
+    <MaxScaleDenominator>750000</MaxScaleDenominator>
+    <MinScaleDenominator>400000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="0.5" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>1500000</MaxScaleDenominator><MinScaleDenominator>750000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="0.6"/>
+    <MaxScaleDenominator>1500000</MaxScaleDenominator>
+    <MinScaleDenominator>750000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="0.6" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>3000000</MaxScaleDenominator><MinScaleDenominator>1500000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="0.7"/>
+    <MaxScaleDenominator>3000000</MaxScaleDenominator>
+    <MinScaleDenominator>1500000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="0.7" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>6500000</MaxScaleDenominator><MinScaleDenominator>3000000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="0.8"/>
+    <MaxScaleDenominator>6500000</MaxScaleDenominator>
+    <MinScaleDenominator>3000000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="0.8" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>12500000</MaxScaleDenominator><MinScaleDenominator>6500000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="0.9"/>
+    <MaxScaleDenominator>12500000</MaxScaleDenominator>
+    <MinScaleDenominator>6500000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="0.9" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>25000000</MaxScaleDenominator><MinScaleDenominator>12500000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="1"/>
+    <MaxScaleDenominator>25000000</MaxScaleDenominator>
+    <MinScaleDenominator>12500000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="1" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>100000000</MaxScaleDenominator><MinScaleDenominator>50000000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="1.25"/>
+    <MaxScaleDenominator>50000000</MaxScaleDenominator>
+    <MinScaleDenominator>25000000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="1.25" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>50000000</MaxScaleDenominator><MinScaleDenominator>25000000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="1.25"/>
+    <MaxScaleDenominator>100000000</MaxScaleDenominator>
+    <MinScaleDenominator>50000000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="1.25" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>200000000</MaxScaleDenominator><MinScaleDenominator>100000000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="1.5"/>
+    <MaxScaleDenominator>200000000</MaxScaleDenominator>
+    <MinScaleDenominator>100000000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="1.5" />
   </Rule>
   <Rule>
-    <MaxScaleDenominator>500000000</MaxScaleDenominator><MinScaleDenominator>200000000</MinScaleDenominator>
-    <LineSymbolizer stroke-width="2"/>
+    <MaxScaleDenominator>500000000</MaxScaleDenominator>
+    <MinScaleDenominator>200000000</MinScaleDenominator>
+    <LineSymbolizer stroke-width="2" />
   </Rule>
 </Style>
 <Layer
-   name="countries"
-   srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs">
+      name="countries"
+   srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over">
     <StyleName>countries</StyleName>
     <Datasource>
-       <Parameter name="file">[absolute path]</Parameter>
-       <Parameter name="type">shape</Parameter>
+       <Parameter name="file"><![CDATA[[absolute path]]]></Parameter>
+       <Parameter name="type"><![CDATA[shape]]></Parameter>
     </Datasource>
   </Layer>