diff --git a/docs/progress.html b/docs/progress.html
index 2d6539cb..11560a5a 100644
--- a/docs/progress.html
+++ b/docs/progress.html
@@ -151,7 +151,7 @@ thead th {text-align:left;padding:0.1em;background-color:#EEE;}
 <tr class="css1"><td>font</td><td>SHORTHAND</td></tr>
 <tr class="css1"><td>font-family</td><td>CSS validator may complain if fallback font
     family not specified</td></tr>
-<tr class="css1"><td>font-size</td><td>COMPOSITE(&lt;absolute-size&gt;,
+<tr class="css1 impl-yes"><td>font-size</td><td>COMPOSITE(&lt;absolute-size&gt;,
     &lt;relative-size&gt;, &lt;length&gt;, &lt;percentage&gt;)</td></tr>
 <tr class="css1 impl-yes"><td>font-style</td><td>ENUM(normal, italic, oblique)</td></tr>
 <tr class="css1 impl-yes"><td>font-variant</td><td>ENUM(normal, small-caps)</td></tr>
diff --git a/library/HTMLPurifier/AttrDef/Percentage.php b/library/HTMLPurifier/AttrDef/Percentage.php
new file mode 100644
index 00000000..9c9ba4fe
--- /dev/null
+++ b/library/HTMLPurifier/AttrDef/Percentage.php
@@ -0,0 +1,34 @@
+<?php
+
+require_once 'HTMLPurifier/AttrDef.php';
+require_once 'HTMLPurifier/AttrDef/Number.php';
+
+class HTMLPurifier_AttrDef_Percentage extends HTMLPurifier_AttrDef
+{
+    
+    var $number_def;
+    
+    function HTMLPurifier_AttrDef_Percentage($non_negative = false) {
+        $this->number_def = new HTMLPurifier_AttrDef_Number($non_negative);
+    }
+    
+    function validate($string, $config, &$context) {
+        
+        $string = $this->parseCDATA($string);
+        
+        if ($string === '') return false;
+        $length = strlen($string);
+        if ($length === 1) return false;
+        if ($string[$length - 1] !== '%') return false;
+        
+        $number = substr($string, 0, $length - 1);
+        $number = $this->number_def->validate($number, $config, $context);
+        
+        if ($number === false) return false;
+        return "$number%";
+        
+    }
+    
+}
+
+?>
\ No newline at end of file
diff --git a/library/HTMLPurifier/CSSDefinition.php b/library/HTMLPurifier/CSSDefinition.php
index 43e9439b..9ff09b78 100644
--- a/library/HTMLPurifier/CSSDefinition.php
+++ b/library/HTMLPurifier/CSSDefinition.php
@@ -77,12 +77,21 @@ class HTMLPurifier_CSSDefinition
             new HTMLPurifier_AttrDef_CSSLength()
         ));
         
+        $this->info['font-size'] = new HTMLPurifier_AttrDef_Composite(array(
+            new HTMLPurifier_AttrDef_Enum(array('xx-small', 'x-small',
+                'small', 'medium', 'large', 'x-large', 'xx-large',
+                'larger', 'smaller')),
+            new HTMLPurifier_AttrDef_Percentage(),
+            new HTMLPurifier_AttrDef_CSSLength()
+        ));
+        
+        
+        
         // this could use specialized code
         $this->info['font-weight'] = new HTMLPurifier_AttrDef_Enum(
             array('normal', 'bold', 'bolder', 'lighter', '100', '200', '300',
             '400', '500', '600', '700', '800', '900'), false);
         
-        
     }
     
 }
diff --git a/tests/HTMLPurifier/AttrDef/CSSTest.php b/tests/HTMLPurifier/AttrDef/CSSTest.php
index 3efa21f5..36eecfbb 100644
--- a/tests/HTMLPurifier/AttrDef/CSSTest.php
+++ b/tests/HTMLPurifier/AttrDef/CSSTest.php
@@ -31,6 +31,9 @@ class HTMLPurifier_AttrDef_CSSTest extends HTMLPurifier_AttrDefHarness
         $this->assertDef('letter-spacing:2px;');
         $this->assertDef('word-spacing:normal;');
         $this->assertDef('word-spacing:3em;');
+        $this->assertDef('font-size:200%;');
+        $this->assertDef('font-size:larger;');
+        $this->assertDef('font-size:12pt;');
         
         // duplicates
         $this->assertDef('text-align:right;text-align:left;',
diff --git a/tests/HTMLPurifier/AttrDef/PercentageTest.php b/tests/HTMLPurifier/AttrDef/PercentageTest.php
new file mode 100644
index 00000000..166cd24f
--- /dev/null
+++ b/tests/HTMLPurifier/AttrDef/PercentageTest.php
@@ -0,0 +1,26 @@
+<?php
+
+require_once 'HTMLPurifier/AttrDef/Percentage.php';
+
+class HTMLPurifier_AttrDef_PercentageTest extends HTMLPurifier_AttrDefHarness
+{
+    
+    function test() {
+        
+        $this->def = new HTMLPurifier_AttrDef_Percentage();
+        
+        $this->assertDef('10%');
+        $this->assertDef('1.607%');
+        $this->assertDef('-567%');
+        
+        $this->assertDef(' 100% ', '100%');
+        
+        $this->assertDef('5', false);
+        $this->assertDef('asdf', false);
+        $this->assertDef('%', false);
+        
+    }
+    
+}
+
+?>
\ No newline at end of file
diff --git a/tests/index.php b/tests/index.php
index d8b477a9..a7a66b2b 100644
--- a/tests/index.php
+++ b/tests/index.php
@@ -69,6 +69,7 @@ $test_files[] = 'AttrDef/ColorTest.php';
 $test_files[] = 'AttrDef/IntegerTest.php';
 $test_files[] = 'AttrDef/NumberTest.php';
 $test_files[] = 'AttrDef/CSSLengthTest.php';
+$test_files[] = 'AttrDef/PercentageTest.php';
 $test_files[] = 'IDAccumulatorTest.php';
 $test_files[] = 'TagTransformTest.php';
 $test_files[] = 'AttrTransform/LangTest.php';