Cleanup texts and comments

core/src/main/java/org/jivesoftware/smack/filter/AndFilter.java

@@ -51,11 +51,11 @@ public class AndFilter implements PacketFilter {
      */
     public AndFilter(PacketFilter... filters) {
         if (filters == null) {
-            throw new IllegalArgumentException("Parameter cannot be null.");
+            throw new IllegalArgumentException("Parameter must not be null.");
         }
         for(PacketFilter filter : filters) {
             if(filter == null) {
-                throw new IllegalArgumentException("Parameter cannot be null.");
+                throw new IllegalArgumentException("Parameter must not be null.");
             }
         }
         this.filters = new ArrayList<PacketFilter>(Arrays.asList(filters));
@@ -69,7 +69,7 @@ public class AndFilter implements PacketFilter {
      */
     public void addFilter(PacketFilter filter) {
         if (filter == null) {
-            throw new IllegalArgumentException("Parameter cannot be null.");
+            throw new IllegalArgumentException("Parameter must not be null.");
         }
         filters.add(filter);
     }

core/src/main/java/org/jivesoftware/smack/filter/NotFilter.java

@@ -36,7 +36,7 @@ public class NotFilter implements PacketFilter {
      */
     public NotFilter(PacketFilter filter) {
         if (filter == null) {
-            throw new IllegalArgumentException("Parameter cannot be null.");
+            throw new IllegalArgumentException("Parameter must not be null.");
         }
         this.filter = filter;
     }

core/src/main/java/org/jivesoftware/smack/filter/OrFilter.java

@@ -51,11 +51,11 @@ public class OrFilter implements PacketFilter {
      */
     public OrFilter(PacketFilter... filters) {
         if (filters == null) {
-            throw new IllegalArgumentException("Parameter cannot be null.");
+            throw new IllegalArgumentException("Parameter must not be null.");
         }
         for(PacketFilter filter : filters) {
             if(filter == null) {
-                throw new IllegalArgumentException("Parameter cannot be null.");
+                throw new IllegalArgumentException("Parameter must not be null.");
             }
         }
         this.filters = new ArrayList<PacketFilter>(Arrays.asList(filters));
@@ -69,7 +69,7 @@ public class OrFilter implements PacketFilter {
      */
     public void addFilter(PacketFilter filter) {
         if (filter == null) {
-            throw new IllegalArgumentException("Parameter cannot be null.");
+            throw new IllegalArgumentException("Parameter must not be null.");
         }
         filters.add(filter);
     }

core/src/main/java/org/jivesoftware/smack/filter/PacketFilter.java

@@ -20,24 +20,22 @@ package org.jivesoftware.smack.filter;
 import org.jivesoftware.smack.packet.Packet;
 
 /**
- * Defines a way to filter packets for particular attributes. Packet filters are
+ * Defines a way to filter packets for particular attributes. Packet filters are used when
- * used when constructing packet listeners or collectors -- the filter defines
+ * constructing packet listeners or collectors -- the filter defines what packets match the criteria
- * what packets match the criteria of the collector or listener for further
+ * of the collector or listener for further packet processing.
- * packet processing.<p>
+ * <p>
- *
+ * Several simple filters are pre-defined. These filters can be logically combined for more complex
- * Several pre-defined filters are defined. These filters can be logically combined
+ * packet filtering by using the {@link org.jivesoftware.smack.filter.AndFilter AndFilter} and
- * for more complex packet filtering by using the
+ * {@link org.jivesoftware.smack.filter.OrFilter OrFilter} filters. It's also possible to define
- * {@link org.jivesoftware.smack.filter.AndFilter AndFilter} and
+ * your own filters by implementing this interface. The code example below creates a trivial filter
- * {@link org.jivesoftware.smack.filter.OrFilter OrFilter} filters. It's also possible
+ * for packets with a specific ID (real code should use {@link PacketIDFilter} instead).
- * to define your own filters by implementing this interface. The code example below
- * creates a trivial filter for packets with a specific ID.
  *
  * <pre>
  * // Use an anonymous inner class to define a packet filter that returns
- * // all packets that have a packet ID of "RS145".
+ * // all packets that have a packet ID of &quot;RS145&quot;.
  * PacketFilter myFilter = new PacketFilter() {
  *     public boolean accept(Packet packet) {
- *         return "RS145".equals(packet.getPacketID());
+ *         return &quot;RS145&quot;.equals(packet.getPacketID());
  *     }
  * };
  * // Create a new packet collector using the filter we created.

core/src/main/java/org/jivesoftware/smack/filter/PacketIDFilter.java

@@ -35,7 +35,7 @@ public class PacketIDFilter implements PacketFilter {
      */
     public PacketIDFilter(String packetID) {
         if (packetID == null) {
-            throw new IllegalArgumentException("Packet ID cannot be null.");
+            throw new IllegalArgumentException("Packet ID must not be null.");
         }
         this.packetID = packetID;
     }

core/src/main/java/org/jivesoftware/smack/filter/ThreadFilter.java

@@ -36,7 +36,7 @@ public class ThreadFilter implements PacketFilter {
      */
     public ThreadFilter(String thread) {
         if (thread == null) {
-            throw new IllegalArgumentException("Thread cannot be null.");
+            throw new IllegalArgumentException("Thread must not be null.");
         }
         this.thread = thread;
     }

core/src/main/java/org/jivesoftware/smack/packet/Packet.java

@@ -235,8 +235,8 @@ public abstract class Packet {
 
     /**
      * Returns the first packet extension that matches the specified element name and
-     * namespace, or <tt>null</tt> if it doesn't exist. If the provided elementName is null
+     * namespace, or <tt>null</tt> if it doesn't exist. If the provided elementName is null,
-     * than only the provided namespace is attempted to be matched. Packet extensions are
+     * only the namespace is matched. Packet extensions are
      * are arbitrary XML sub-documents in standard XMPP packets. By default, a 
      * DefaultPacketExtension instance will be returned for each extension. However, 
      * PacketExtensionProvider instances can be registered with the