diff --git a/docs/manual/CoreTasks/style.html b/docs/manual/CoreTasks/style.html
index de184d734..a8f11b832 100644
--- a/docs/manual/CoreTasks/style.html
+++ b/docs/manual/CoreTasks/style.html
@@ -187,9 +187,20 @@ element is used to perform Entity and URI resolution.</p>
   <tr>
     <td valign="top">expression</td>
     <td valign="top">Text value to be placed into the param.<br/>
-    Was originally intended to be an XSL expression.
+    Was originally intended to be an XSL expression.</td>
     <td align="center" valign="top">Yes</td>
   </tr>
+  <tr>
+    <td valign="top">if</td>
+    <td valign="top">The param will only passed if this property is set.</td>
+    <td align="center" valign="top">No</td>
+  </tr>
+  <tr>
+    <td valign="top">unless</td>
+    <td valign="top">The param will only passed unless this property is set.</td>
+    <td align="center" valign="top">No</td>
+  </tr>
+
 </table>
 
 <h4>outputproperty ('trax' processors only)</h4>
@@ -230,7 +241,7 @@ Used to specify factory settings.
     transformer factory to use. For example
       <tt>org.apache.xalan.processor.TransformerFactoryImpl</tt>
        or <tt>org.apache.xalan.xsltc.trax.TransformerFactoryImpl</tt>
-       or <tt>net.sf.saxon.TransformerFactoryImpl</tt>...    
+       or <tt>net.sf.saxon.TransformerFactoryImpl</tt>...
     </td>
     <td align="center" valign="top">No. Defaults to the JAXP lookup mechanism.</td>
   </tr>
@@ -318,7 +329,7 @@ And in Saxon 7.x:
   <h4>Using factory settings</h4>
 <pre>&lt;xslt in=&quot;doc.xml&quot; out=&quot;build/doc/output.xml&quot;
       style=&quot;style/apache.xsl&quot;&gt;
-  &lt;factory name=&quot;org.apache.xalan.processor.TransformerFactoryImpl&quot;&gt;  
+  &lt;factory name=&quot;org.apache.xalan.processor.TransformerFactoryImpl&quot;&gt;
     &lt;attribute name=&quot;http://xml.apache.org/xalan/features/optimize&quot; value=&quot;true&quot;/&gt;
   &lt;/factory&gt;
 &lt;/xslt&gt;</pre>
@@ -329,4 +340,3 @@ Reserved.</p>
 
 </body>
 </html>
-
diff --git a/src/etc/testcases/taskdefs/style/build.xml b/src/etc/testcases/taskdefs/style/build.xml
new file mode 100644
index 000000000..dde2b9b1d
--- /dev/null
+++ b/src/etc/testcases/taskdefs/style/build.xml
@@ -0,0 +1,45 @@
+<?xml version="1.0"?>
+
+<project name="style-test" basedir="." default="nothing">
+
+  <property name="out.dir" value="out"/>
+
+
+  <target name="setup">
+  </target>
+
+  <target name="teardown">
+      <delete dir="${out.dir}" failonerror="false" />
+  </target>
+
+  <target name="testStyleIsSet">
+      <style in="data.xml" out="${out.dir}/out.xml"/>
+  </target>
+
+  <target name="testTransferParameterSet">
+      <property name="value" value="myvalue"/>
+      <style in="data.xml" out="${out.dir}/out.xml" style="printParams.xsl">
+          <param name="set" expression="${value}"/>
+      </style>
+  </target>
+
+  <target name="testTransferParameterEmpty">
+      <property name="value" value=""/>
+      <style in="data.xml" out="${out.dir}/out.xml" style="printParams.xsl">
+          <param name="empty" expression="${value}"/>
+      </style>
+  </target>
+
+  <target name="testTransferParameterUnset">
+      <style in="data.xml" out="${out.dir}/out.xml" style="printParams.xsl">
+          <param name="undefined" expression="${value}"/>
+      </style>
+  </target>
+
+  <target name="testTransferParameterUnsetWithIf">
+      <style in="data.xml" out="${out.dir}/out.xml" style="printParams.xsl">
+          <param name="undefined" expression="${value}" if="value" />
+      </style>
+  </target>
+
+</project>
\ No newline at end of file
diff --git a/src/etc/testcases/taskdefs/style/data.xml b/src/etc/testcases/taskdefs/style/data.xml
new file mode 100644
index 000000000..b86e0c064
--- /dev/null
+++ b/src/etc/testcases/taskdefs/style/data.xml
@@ -0,0 +1 @@
+<data/>
\ No newline at end of file
diff --git a/src/etc/testcases/taskdefs/style/printParams.xsl b/src/etc/testcases/taskdefs/style/printParams.xsl
new file mode 100644
index 000000000..1d8728e42
--- /dev/null
+++ b/src/etc/testcases/taskdefs/style/printParams.xsl
@@ -0,0 +1,20 @@
+<?xml version="1.0"?>
+
+<xsl:stylesheet
+  version="1.0"
+  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+  xmlns:fo="http://www.w3.org/1999/XSL/Format">
+
+<!-- get the xsl-parameter -->
+<xsl:param name="set">set default value</xsl:param>
+<xsl:param name="empty">empty default value</xsl:param>
+<xsl:param name="undefined">undefined default value</xsl:param>
+
+<!-- use the xsl-parameter -->
+<xsl:template match="/">
+set='<xsl:value-of select="$set"/>'
+empty='<xsl:value-of select="$empty"/>'
+undefined='<xsl:value-of select="$undefined"/>'
+</xsl:template>
+
+</xsl:stylesheet>
\ No newline at end of file
diff --git a/src/main/org/apache/tools/ant/taskdefs/XSLTProcess.java b/src/main/org/apache/tools/ant/taskdefs/XSLTProcess.java
index 6a0a2eb0f..b06dfd20c 100644
--- a/src/main/org/apache/tools/ant/taskdefs/XSLTProcess.java
+++ b/src/main/org/apache/tools/ant/taskdefs/XSLTProcess.java
@@ -615,6 +615,19 @@ public class XSLTProcess extends MatchingTask implements XSLTLogger {
         /** The parameter's value */
         private String expression = null;
 
+        private String ifProperty;
+        private String unlessProperty;
+        private Project project;
+
+        /**
+         * Set the current project
+         *
+         * @param project the current project
+         */
+        public void setProject(Project project) {
+            this.project = project;
+        }
+
         /**
          * Set the parameter name.
          *
@@ -658,6 +671,39 @@ public class XSLTProcess extends MatchingTask implements XSLTLogger {
             }
             return expression;
         }
+
+        /**
+         * Set whether this param should be used.  It will be
+         * used if the property has been set, otherwise it won't.
+         * @param ifProperty name of property
+         */
+        public void setIf(String ifProperty) {
+            this.ifProperty = ifProperty;
+        }
+
+        /**
+         * Set whether this param should NOT be used. It
+         * will not be used if the property has been set, orthwise it
+         * will be used.
+         * @param unlessProperty name of property
+         */
+        public void setUnless(String unlessProperty) {
+            this.unlessProperty = unlessProperty;
+        }
+        /**
+         * Ensures that the param passes the conditions placed
+         * on it with <code>if</code> and <code>unless</code> properties.
+         */
+        public boolean shouldUse() {
+            if (ifProperty != null && project.getProperty(ifProperty) == null) {
+                return false;
+            } else if (unlessProperty != null
+                    && project.getProperty(unlessProperty) != null) {
+                return false;
+            }
+            
+            return true;
+        }
     } // Param
 
 
@@ -743,7 +789,9 @@ public class XSLTProcess extends MatchingTask implements XSLTLogger {
             liaison.setStylesheet(stylesheet);
             for (Enumeration e = params.elements(); e.hasMoreElements();) {
                 Param p = (Param) e.nextElement();
-                liaison.addParam(p.getName(), p.getExpression());
+                if (p.shouldUse()) {
+                    liaison.addParam(p.getName(), p.getExpression());
+                }
             }
             if (liaison instanceof TraXLiaison) {
                 configureTraXLiaison((TraXLiaison) liaison);
diff --git a/src/testcases/org/apache/tools/ant/taskdefs/StyleTest.java b/src/testcases/org/apache/tools/ant/taskdefs/StyleTest.java
new file mode 100644
index 000000000..75a5c16f7
--- /dev/null
+++ b/src/testcases/org/apache/tools/ant/taskdefs/StyleTest.java
@@ -0,0 +1,154 @@
+/*
+ * The Apache Software License, Version 1.1
+ *
+ * Copyright (c) 2001-2002 The Apache Software Foundation.  All rights
+ * reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. The end-user documentation included with the redistribution, if
+ *    any, must include the following acknowlegement:
+ *       "This product includes software developed by the
+ *        Apache Software Foundation (http://www.apache.org/)."
+ *    Alternately, this acknowlegement may appear in the software itself,
+ *    if and wherever such third-party acknowlegements normally appear.
+ *
+ * 4. The names "Ant" and "Apache Software
+ *    Foundation" must not be used to endorse or promote products derived
+ *    from this software without prior written permission. For written
+ *    permission, please contact apache@apache.org.
+ *
+ * 5. Products derived from this software may not be called "Apache"
+ *    nor may "Apache" appear in their names without prior written
+ *    permission of the Apache Group.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ */
+package org.apache.tools.ant.taskdefs;
+
+
+import org.apache.tools.ant.BuildFileTest;
+import org.apache.tools.ant.util.FileUtils;
+
+import java.io.File;
+import java.io.FileReader;
+import java.io.IOException;
+import java.io.Reader;
+
+
+/**
+ * TestCases für <style> / <xslt> task.
+ * @author Jan Matèrne
+ * @version 2003-08-05
+ */
+public class StyleTest extends BuildFileTest {
+
+    public StyleTest(String s) {
+        super(s);
+    }
+
+    protected void setUp() throws Exception {
+        configureProject("src/etc/testcases/taskdefs/style/build.xml");
+        //executeTarget("setup");
+        //commented out for performance while target is empty
+    }
+
+    protected void tearDown() throws Exception {
+        executeTarget("teardown");
+    }
+
+    public void testStyleIsSet() throws Exception {
+        expectBuildException("testStyleIsSet", "no stylesheet specified");
+    }
+
+    public void testTransferParameterSet() throws Exception {
+        expectFileContains("testTransferParameterSet",  // target
+                           "out/out.xml",               // file
+                           "set='myvalue'");            // exptected string
+    }
+
+    public void testTransferParameterEmpty() throws Exception {
+        expectFileContains("testTransferParameterEmpty",
+                           "out/out.xml",
+                           "empty=''");
+    }
+
+    public void testTransferParameterUnset() throws Exception {
+        expectFileContains("testTransferParameterUnset",
+                           "out/out.xml",
+                           "undefined='${value}'");
+    }
+
+    public void testTransferParameterUnsetWithIf() throws Exception {
+        expectFileContains("testTransferParameterUnsetWithIf",
+                           "out/out.xml",
+                           "undefined='undefined default value'");
+    }
+
+
+    // *************  copied from ConcatTest  *************
+
+    // ------------------------------------------------------
+    //   Helper methods - should be in BuildFileTest
+    // -----------------------------------------------------
+
+    private String getFileString(String filename)
+        throws IOException
+    {
+        Reader r = null;
+        try {
+            r = new FileReader(getProject().resolveFile(filename));
+            return  FileUtils.newFileUtils().readFully(r);
+        }
+        finally {
+            try {r.close();} catch (Throwable ignore) {}
+        }
+
+    }
+
+    private String getFileString(String target, String filename)
+        throws IOException
+    {
+        executeTarget(target);
+        return getFileString(filename);
+    }
+
+    private void expectFileContains(
+        String target, String filename, String contains)
+        throws IOException
+    {
+        String content = getFileString(target, filename);
+        assertTrue(
+            "expecting file " + filename + " to contain " +
+            contains +
+            " but got " + content, content.indexOf(contains) > -1);
+    }
+
+}
\ No newline at end of file