Index: lucene/analysis/common/src/test/org/apache/lucene/analysis/core/TestStopFilterFactory.java
===================================================================
--- lucene/analysis/common/src/test/org/apache/lucene/analysis/core/TestStopFilterFactory.java	(revision 1524128)
+++ lucene/analysis/common/src/test/org/apache/lucene/analysis/core/TestStopFilterFactory.java	(working copy)
@@ -57,6 +57,11 @@
     assertTrue(words.contains("her"));
     assertTrue(words.contains("hers"));
     assertTrue(words.contains("herself"));
+
+    // defaults
+    factory = (StopFilterFactory) tokenFilterFactory("Stop");
+    assertEquals(StopAnalyzer.ENGLISH_STOP_WORDS_SET, factory.getStopWords());
+    assertEquals(false, factory.isIgnoreCase());
   }
   
   /** Test that bogus arguments result in exception */
@@ -68,4 +73,30 @@
       assertTrue(expected.getMessage().contains("Unknown parameters"));
     }
   }
+
+  /** Test that bogus arguments result in exception */
+  public void testBogusFormats() throws Exception {
+    try {
+      tokenFilterFactory("Stop", 
+                         "words", "stop-snowball.txt",
+                         "format", "bogus");
+      fail();
+    } catch (IllegalArgumentException expected) {
+      String msg = expected.getMessage();
+      assertTrue(msg, msg.contains("Unknown"));
+      assertTrue(msg, msg.contains("format"));
+      assertTrue(msg, msg.contains("bogus"));
+    }
+    try {
+      tokenFilterFactory("Stop", 
+                         // implicit default words file
+                         "format", "bogus");
+      fail();
+    } catch (IllegalArgumentException expected) {
+      String msg = expected.getMessage();
+      assertTrue(msg, msg.contains("can not be specified"));
+      assertTrue(msg, msg.contains("format"));
+      assertTrue(msg, msg.contains("bogus"));
+    }
+  }
 }
Index: lucene/analysis/common/src/java/org/apache/lucene/analysis/core/StopFilterFactory.java
===================================================================
--- lucene/analysis/common/src/java/org/apache/lucene/analysis/core/StopFilterFactory.java	(revision 1524128)
+++ lucene/analysis/common/src/java/org/apache/lucene/analysis/core/StopFilterFactory.java	(working copy)
@@ -22,22 +22,57 @@
 import org.apache.lucene.analysis.util.ResourceLoader;
 import org.apache.lucene.analysis.util.ResourceLoaderAware;
 import org.apache.lucene.analysis.util.TokenFilterFactory;
+import org.apache.lucene.analysis.util.WordlistLoader; // jdocs
 
 import java.util.Map;
 import java.io.IOException;
 
 /**
  * Factory for {@link StopFilter}.
+ *
  * <pre class="prettyprint">
  * &lt;fieldType name="text_stop" class="solr.TextField" positionIncrementGap="100" autoGeneratePhraseQueries="true"&gt;
  *   &lt;analyzer&gt;
  *     &lt;tokenizer class="solr.WhitespaceTokenizerFactory"/&gt;
  *     &lt;filter class="solr.StopFilterFactory" ignoreCase="true"
- *             words="stopwords.txt"
+ *             words="stopwords.txt" format="wordset"
  *   &lt;/analyzer&gt;
  * &lt;/fieldType&gt;</pre>
+ *
+ * <p>
+ * All attributes are optional:
+ * </p>
+ * <ul>
+ *  <li><code>ignoreCase</code> defaults to <code>false</code></li>
+ *  <li><code>words</code> should be the name of a stopwords file to parse, if not 
+ *      specified the factory will use {@link StopAnalyzer#ENGLISH_STOP_WORDS_SET}
+ *  </li>
+ *  <li><code>format</code> defines how the <code>words</code> file will be parsed, 
+ *      and defaults to <code>wordset</code>.  If <code>words</code> is not specified, 
+ *      then <code>format</code> must not be specified.
+ *  </li>
+ * </ul>
+ * <p>
+ * The valid values for the <code>format</code> option are:
+ * </p>
+ * <ul>
+ *  <li><code>wordset</code> - This is the default format, which supports one word per 
+ *      line (including any intra-word whitespace) and allows whole line comments 
+ *      begining with the "#" character.  Blank lines are ignored.  See 
+ *      {@link WordlistLoader#getLines WordlistLoader.getLines} for details.
+ *  </li>
+ *  <li><code>snowball</code> - This format allows for multiple words specified on each 
+ *      line, and trailing comments may be specified using the vertical line ("&#124;"). 
+ *      Blank lines are ignored.  See 
+ *      {@link WordlistLoader#getSnowballWordSet WordlistLoader.getSnowballWordSet} 
+ *      for details.
+ *  </li>
+ * </ul>
  */
 public class StopFilterFactory extends TokenFilterFactory implements ResourceLoaderAware {
+  public static final String FORMAT_WORDSET = "wordset";
+  public static final String FORMAT_SNOWBALL = "snowball";
+  
   private CharArraySet stopWords;
   private final String stopWordFiles;
   private final String format;
@@ -48,7 +83,7 @@
     super(args);
     assureMatchVersion();
     stopWordFiles = get(args, "words");
-    format = get(args, "format");
+    format = get(args, "format", (null == stopWordFiles ? null : FORMAT_WORDSET));
     ignoreCase = getBoolean(args, "ignoreCase", false);
     if (!args.isEmpty()) {
       throw new IllegalArgumentException("Unknown parameters: " + args);
@@ -58,12 +93,17 @@
   @Override
   public void inform(ResourceLoader loader) throws IOException {
     if (stopWordFiles != null) {
-      if ("snowball".equalsIgnoreCase(format)) {
+      if (FORMAT_WORDSET.equalsIgnoreCase(format)) {
+        stopWords = getWordSet(loader, stopWordFiles, ignoreCase);
+      } else if (FORMAT_SNOWBALL.equalsIgnoreCase(format)) {
         stopWords = getSnowballWordSet(loader, stopWordFiles, ignoreCase);
       } else {
-        stopWords = getWordSet(loader, stopWordFiles, ignoreCase);
+        throw new IllegalArgumentException("Unknown 'format' specified for 'words' file: " + format);
       }
     } else {
+      if (null != format) {
+        throw new IllegalArgumentException("'format' can not be specified w/o an explicit 'words' file: " + format);
+      }
       stopWords = new CharArraySet(luceneMatchVersion, StopAnalyzer.ENGLISH_STOP_WORDS_SET, ignoreCase);
     }
   }