diff --git a/library/HTMLPurifier/AttrDef/URI.php b/library/HTMLPurifier/AttrDef/URI.php
new file mode 100644
index 00000000..ffda0e71
--- /dev/null
+++ b/library/HTMLPurifier/AttrDef/URI.php
@@ -0,0 +1,93 @@
+<?php
+
+require_once 'HTMLPurifier/URIScheme.php';
+require_once 'HTMLPurifier/URISchemeRegistry.php';
+
+class HTMLPurifier_AttrDef_URI extends HTMLPurifier_AttrDef
+{
+    function validate($uri, $config = null) {
+        
+        // We'll write stack-based parsers later, for now, use regexps to
+        // get things working as fast as possible (irony)
+        
+        // parse as CDATA
+        $uri = $this->parseCDATA($uri);
+        
+        // while it would be nice to use parse_url(), that's specifically
+        // for HTTP and thus won't work for our generic URI parsing
+        
+        // according to the RFC... (but this cuts corners, i.e. non-validating)
+        $regexp = '!^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?!';
+        //           12            3  4          5       6  7        8 9
+        $matches = array();
+        
+        $result = preg_match($regexp, $uri, $matches);
+        
+        if (!$result) return ''; // wow, that's very strange
+        
+        // seperate out parts
+        $scheme     = !empty($matches[1]) ? $matches[2] : null;
+        $authority  = !empty($matches[3]) ? $matches[4] : null;
+        $path       = $matches[5]; // always present
+        $query      = !empty($matches[6]) ? $matches[7] : null;
+        $fragment   = !empty($matches[8]) ? $matches[9] : null;
+        
+        // okay, no need to validate the scheme since we do that when we
+        // retrieve the specific scheme object from the registry
+        $scheme = ctype_lower($scheme) ? $scheme : strtolower($scheme);
+        $registry = HTMLPurifier_URISchemeRegistry::instance();
+        $scheme_obj = $registry->getScheme($scheme);
+        
+        if (!$scheme_obj) return ''; // invalid scheme, clean it out
+        
+        if ($authority !== null) {
+            // validate authority
+            $matches = array();
+            
+            $HEXDIG = '[A-Fa-f0-9]';
+            $unreserved = 'A-Za-z0-9-._~';
+            $sub_delims = '!$&\'()';
+            $h16 = "{$HEXDIG}{1,4}";
+            $dec_octet = '(?:25[0-5]|2[0-4]\d|1\d\d|1\d|[0-9])';
+            $IPv4address = "$dec_octet.$dec_octet.$dec_octet.$dec_octet";
+            $ls32 = "(?:$h16:$h16|$IPv4address)";
+            $IPvFuture = "v$HEXDIG+\.[:$unreserved$sub_delims]+";
+            $IPv6Address = "(?:".
+                                        "(?:$h16:){6}$ls32" .
+                                     "|::(?:$h16:){5}$ls32" .
+                            "|(?:$h16)?::(?:$h16:){4}$ls32" .
+                "|(?:(?:$h16:){1}$h16)?::(?:$h16:){3}$ls32" .
+                "|(?:(?:$h16:){2}$h16)?::(?:$h16:){2}$ls32" .
+                "|(?:(?:$h16:){3}$h16)?::(?:$h16:){1}$ls32" .
+                "|(?:(?:$h16:){4}$h16)?::$ls32" .
+                "|(?:(?:$h16:){5}$h16)?::$h16" .
+                "|(?:(?:$h16:){6}$h16)?::" .
+                ")";
+            $IP_literal = "\[(?:$IPvFuture|$IPv6Address)\]";
+            $regexp = "/^(([^@]+)@)?(\[$IP_literal\]|[^:]*)(:(\d*))?/";
+            
+            preg_match($regexp, $authority, $matches);
+            $userinfo   = !empty($matches[1]) ? $matches[2] : null;
+            $host       = !empty($matches[3]) ? $matches[3] : null;
+            $port       = !empty($matches[4]) ? $matches[5] : null;
+            
+            if ($port !== null) {
+                if (!ctype_digit($port) || $port < 1 || $port > 65535) {
+                    $port = null;
+                }
+            }
+            $authority =
+                ($userinfo === null ? '' : ($userinfo . '@')) .
+                $host .
+                ($port === null ? '' : (':' . $port));
+        }
+        
+        list($authority, $path, $query, $fragment) = 
+        $scheme_obj->validateComponents($authority, $path, $query, $fragment);
+        
+        
+        
+    }
+}
+
+?>
\ No newline at end of file
diff --git a/library/HTMLPurifier/URIScheme.php b/library/HTMLPurifier/URIScheme.php
new file mode 100644
index 00000000..8b3ec2c1
--- /dev/null
+++ b/library/HTMLPurifier/URIScheme.php
@@ -0,0 +1,12 @@
+<?php
+
+class HTMLPurifier_URIScheme
+{
+    
+    function validateComponents() {
+        
+    }
+    
+}
+
+?>
\ No newline at end of file
diff --git a/library/HTMLPurifier/URISchemeRegistry.php b/library/HTMLPurifier/URISchemeRegistry.php
new file mode 100644
index 00000000..438561be
--- /dev/null
+++ b/library/HTMLPurifier/URISchemeRegistry.php
@@ -0,0 +1,23 @@
+<?php
+
+class HTMLPurifier_URISchemeRegistry
+{
+    
+    // pass a registry object $prototype with a compatible interface and
+    // the function will copy it and return it all further times.
+    // pass bool true to reset to the default registry
+    function &instance($prototype = null) {
+        static $instance = null;
+        if ($prototype !== null) {
+            $instance = $prototype;
+        } elseif ($instance === null || $prototype == true) {
+            $instance = new HTMLPurifier_URISchemeRegistry();
+        }
+        return $instance;
+    }
+    
+    function &getScheme($scheme) {}
+    
+}
+
+?>
\ No newline at end of file
diff --git a/tests/HTMLPurifier/AttrDef/URITest.php b/tests/HTMLPurifier/AttrDef/URITest.php
new file mode 100644
index 00000000..32b397fc
--- /dev/null
+++ b/tests/HTMLPurifier/AttrDef/URITest.php
@@ -0,0 +1,183 @@
+<?php
+
+require_once 'HTMLPurifier/AttrDefHarness.php';
+require_once 'HTMLPurifier/AttrDef/URI.php';
+
+// WARNING: INCOMPLETE UNIT TESTS!
+// we are currently abstaining IPv6 and percent-encode fixing unit tests
+// as well as recomposition tests
+
+class HTMLPurifier_AttrDef_URITest extends HTMLPurifier_AttrDefHarness
+{
+    
+    function testGenericURI() {
+        
+        generate_mock_once('HTMLPurifier_URIScheme');
+        generate_mock_once('HTMLPurifier_URISchemeRegistry');
+        
+        // finally, lets get a copy of the actual class
+        $def = new HTMLPurifier_AttrDef_URI();
+        
+        // initialize test inputs
+        $uri = // input URI
+        $components = // what components the URI should be parsed to
+        $return_components = // return components
+        $expect_uri = array(); // what reassembled URI to expect
+        
+        //////////////////////////////////////////////////////////////////////
+        
+        // test a regular instance, return identical URI
+        $uri[0] = 'http://www.example.com/webhp?q=foo#result2';
+        $components[0] = array(
+            'www.example.com',  // authority
+            '/webhp',           // path
+            'q=foo',            // query
+            'result2'           // fragment
+        );
+        
+        // test an amended URI (the actual logic is irrelevant)
+        // test that user and port get parsed correctly (3.2.1 and 3.2.3)
+        $uri[1] = 'http://user@authority.part:80/now/the/path?query#fragment';
+        $components[1] = array(
+            'user@authority.part:80', // yes, user+port are part of authority
+            '/now/the/path', 'query', 'fragment'
+        );
+        $return_components[1] = array( // removed port (it's standard)
+            'user@authority.part', '/now/the/path', 'query', 'fragment'
+        );
+        $expect_uri[1] = 'http://user@authority.part/now/the/path?query#fragment';
+        
+        // percent encoded characters are not resolved during generic URI
+        // parsing even though RFC 3986 defines this notation
+        // also test what happens when query/fragment are missing
+        $uri[2] = 'http://en.wikipedia.org/wiki/Clich%C3%A9';
+        $components[2] = array(
+            'en.wikipedia.org', '/wiki/Clich%C3%A9', null, null
+        );
+        
+        // test distinction between empty query and undefined query (above)
+        $uri[3] = 'http://www.example.com/?#';
+        $components[3] = array( 'www.example.com', '/', '', '' );
+        
+        // path is always defined, even if empty
+        $uri[4] = 'http://www.example.com';
+        $components[4] = array( 'www.example.com', '', null, null );
+        
+        // test parsing of an opaque URI
+        $uri[5] = 'mailto:bob@example.com';
+        $components[5] = array(null, 'bob@example.com', null, null);
+        
+        // even though we don't resolve percent entities, we have to fix
+        // improper percent-encodes. Taken one at a time:
+        // %56 - V, which is an unreserved character
+        // %fc - u with an umlaut, normalize to uppercase
+        // %GJ - invalid characters in entity, encode %
+        // %5 - prematurely terminated, encode %
+        // %FC - u with umlaut, correct
+        // note that Apache doesn't do such fixing, rather, it just claims
+        // that the browser sent a "Bad Request".
+        //$uri[6] = 'http://www.example.com/%56%fc%GJ%5%FC';
+        //$components[6] = array('www.example.com', '/V%FC%25GJ%255%FC', null, null);
+        //$expect_uri[6] = 'http://www.example.com/V%FC%25GJ%255%FC';
+        
+        // test IPv4 address (behavior may vary with configuration)
+        $uri[7] = 'http://192.0.34.166/';
+        $components[7] = array('192.0.34.166', '/', null, null);
+        
+        // while it may look like an IPv4 address, it's really a reg-name.
+        // don't destroy it
+        $uri[8] = 'http://333.123.32.123/';
+        $components[8] = array('333.123.32.123', '/', null, null);
+        
+        // test IPv6 address, using amended form of RFC's example
+        //$uri[9] = 'http://[2001:db8::7]/c=GB?objectClass?one';
+        //$components[9] = array('[2001:db8::7]', '/c=GB', 'objectClass?one', null);
+        
+        // We will not implement punycode encoding, that's up to the browsers
+        // We also will not implement percent to IDNA encoding transformations:
+        // if you need to use an international domain in a link, make sure that
+        // you've got it in UTF-8 and send it in raw (no encoding).
+        
+        // break the RFC a little and allow international characters
+        // WARNING: UTF-8 encoded!
+        $uri[10] = 'http://tūdaliņ.lv';
+        $components[10] = array('tūdaliņ.lv', '', null, null);
+        
+        // test invalid IPv6 address and invalid reg-name
+        //$uri[11] = 'http://[2001:0db8:85z3:08d3:1319:8a2e:0370:7334]';
+        //$components[11] = array(null, '', null, null);
+        
+        // test invalid port
+        $uri[12] = 'http://example.com:foobar';
+        $components[12] = array('example.com', '', null, null);
+        
+        // test overlarge port (max is 65535, although this isn't official)
+        $uri[13] = 'http://example.com:65536';
+        $components[13] = array('example.com', '', null, null);
+        
+        // some spec abnf tests
+        
+        // "authority . path-abempty" omitted, it is a trivial case
+        
+        // "path-absolute", note this is different from path-rootless
+        $uri[14] = 'http:/this/is/path';
+        $components[14] = array(null, '/this/is/path', null, null);
+        $expect_uri[14] = 'http:/this/is/path'; // do not munge scheme off
+        
+        // "path-rootless" - this should not be used but is allowed
+        $uri[15] = 'http:this/is/path';
+        $components[15] = array(null, 'this/is/path', null, null);
+        $expect_uri[15] = 'this/is/path'; // munge scheme off
+        
+        // "path-empty" - a rather interesting case, remove the scheme
+        $uri[16] = 'http:';
+        $components[16] = array(null, '', null, null);
+        $expect_uri[16] = ''; // munge scheme off
+        
+        // test invalid scheme
+        $uri[17] = 'javascript:alert("moo");';
+        $components[17] = false;
+        $expect_uri[17] = '';
+        
+        foreach ($uri as $i => $value) {
+            
+            // $fake_registry isn't the real mock, because due to PHP 4 weirdness
+            // I cannot set a default value to function parameters that are passed
+            // by reference. So we use the value instance() returns.
+            $fake_registry = new HTMLPurifier_URISchemeRegistryMock($this);
+            $registry = HTMLPurifier_URISchemeRegistry::instance($fake_registry);
+            
+            // now, let's at a pseudo-scheme to the registry
+            $scheme = new HTMLPurifier_URISchemeMock($this);
+            
+            // here are the schemes we will support with overloaded mocks
+            $registry->setReturnValue('getScheme', $scheme, array('http'));
+            $registry->setReturnValue('getScheme', $scheme, array('mailto'));
+            
+            // default return value is false (meaning no scheme defined: reject)
+            $registry->setReturnValue('getScheme', false, array('*'));
+            
+            if (!isset($return_components[$i])) {
+                $return_components[$i] = $components[$i];
+            }
+            if (!isset($expect_uri[$i])) {
+                $expect_uri[$i] = $value;
+            }
+            if ($components[$i] === false) {
+                $scheme->expectNever('validateComponents');
+            } else {
+                $scheme->setReturnValue(
+                    'validateComponents', $return_components[$i], $components[$i]);
+                $scheme->expectOnce('validateComponents', $components[$i]);
+            }
+            $result = $def->validate($value);
+            $scheme->tally();
+            //$this->assertIdentical($expect_uri[$i], $result);
+            
+        }
+        
+    }
+    
+}
+
+?>
\ No newline at end of file
diff --git a/tests/index.php b/tests/index.php
index 7c28cdb4..61f5e7f7 100644
--- a/tests/index.php
+++ b/tests/index.php
@@ -62,7 +62,7 @@ $test_files[] = 'AttrDef/LangTest.php';
 $test_files[] = 'AttrDef/PixelsTest.php';
 $test_files[] = 'AttrDef/LengthTest.php';
 $test_files[] = 'AttrDef/NumberSpanTest.php';
-//$test_files[] = 'AttrDef/URITest.php';
+$test_files[] = 'AttrDef/URITest.php';
 $test_files[] = 'IDAccumulatorTest.php';
 $test_files[] = 'TagTransformTest.php';
 $test_files[] = 'AttrTransform/LangTest.php';