Custom Control for "enhanced" validation messages

Update 22.06.2012: Now shows messages not bound to any control. E.g. messages related to using concurrencyMode
Update 08.06.2012: Added sorting routine to get the messages in the same order that they're in the page
Update 22.07.2011: I added functionality to select/focus a dijit tab if the field is inside a dijit.layout.TabContainer. I also added a highlight effect when a field is focused.
Disclaimer: This custom control is not entirely my idea. I've been thinking about doing something like this for a while. After I tried to help with this question by Steve Pridemore in the XPages Development Forum, I found the solution.
The code below can be used as a custom control that is a little bit more advanced (probably has its flaws) than the regular Display Errors control. If the field with a validation error has a label, it shows the label, then the error message. On the label, a link is generated that sets focus to the related field when you click it.

<?xml version="1.0" encoding="UTF-8"?>
<xp:view xmlns:xp="http://www.ibm.com/xsp/core">
 <xp:this.beforeRenderResponse>
  <![CDATA[#{javascript:function addChildrenClientIds(component:javax.faces.component.UIComponentBase, clientIds:java.util.ArrayList) {
 try {
  var children = component.getChildren();
  
  for (var child in children) {
   clientIds.add(child.getClientId(facesContext));
   if (child.getChildCount() > 0) {
    addChildrenClientIds(child, clientIds);
   }
  }
 } catch (e) {
  /*Debug.logException(e);*/
 }
}

try {
 var messageObjects = [];
 var messageClientIds = facesContext.getClientIdsWithMessages(); 
 
 // There are messages for components - Get client ids in sorted order
 if (messageClientIds.hasNext()) {
  var clientIds = new java.util.ArrayList();
  addChildrenClientIds(view, clientIds);
 }
 
 // Used to keep track of which messages are for components
 var componentMessages = new java.util.ArrayList();
 
 while (messageClientIds.hasNext()) {
  var clientId = messageClientIds.next();
  if( !clientId ){ continue; }
  
  var component = view.findComponent( clientId.replace( view.getClientId( facesContext ), '').replace( /\:\d*\:/g, ':') );
  if (!component) { continue; }
  
  // Fetch messages for component
  var message = '',
  messages = facesContext.getMessages( clientId );
  while (messages.hasNext()) {
   var messageItem = messages.next();
   message += (message) ? ', ' : '' + messageItem.getSummary();
   
   componentMessages.push( messageItem );
  }
  
  // If component has label - fetch
  var labelComponent = getLabelFor(component);
  var label = (labelComponent) ? labelComponent.getValue() : '';
  if (!label && component) {
   var id = component.getId();
   if (id.indexOf('_') > 0) {
    label = id;
   }
  }
  
  if (label && label.indexOf(':') === -1) {
   label += ':';
  }
  
  messageObjects.push({
   index : clientIds.indexOf(clientId),
   clientId : clientId,
   label : label,
   message : message
  });
 }
 
 // Sort message object by the order of the components in the page
 messageObjects.sort(function (a, b) {
  if (a.index > b.index) { return 1; }
  if (a.index < b.index) { return -1; }
  return 0;
 });
 
 // Add all (if any) system messages at the top
 var allMessages = facesContext.getMessages();
 while( allMessages.hasNext() ){
  messageItem = allMessages.next();  
  if( !componentMessages.contains( messageItem ) ){   
   messageObjects.unshift({ message: messageItem.getSummary() });
  }
 }
 
 viewScope.messageObjects = messageObjects;
} catch (e) { 
 /*Debug.logException(e);*/
}
}]]></xp:this.beforeRenderResponse>
 <xp:scriptBlock>
  <xp:this.value><![CDATA[var EMessages = {
 // Set focus to field
 setFocus: function( clientId ){
  var matchingFieldsByName = dojo.query('[name=' + clientId + ']');
  if (matchingFieldsByName.length > 0) {
   if (dijit && dijit.registry) {
    this.showDojoTabWithField(clientId);
   }
   var field = matchingFieldsByName[0];
   
   // Workaround for dijit fields
   if( field.getAttribute( 'type' ) === 'hidden' ){
    var matchingFieldsById = dojo.query('input[id=' + clientId + ']');
    field = matchingFieldsById[0];
   }
   
   field.focus();
   dojo.animateProperty({
    duration : 800,
    node : field,
    properties : {
     backgroundColor : {
      start : '#FFFFEE',
      end : dojo.style(field, 'backgroundColor')
     }
    }
   }).play();
  }
  return false;
 },
 
 // If field is inside a dijit/extlib TabContainer - activate
 showDojoTabWithField: function( clientId ){
  dijit.registry.byClass("extlib.dijit.TabContainer").forEach(function (tabContainer) {
   dojo.forEach(tabContainer.getChildren(), function (containerPane) {
    if ( dojo.query( containerPane.containerNode ).query( '[name="' + clientId + '"]' ).length > 0) {
     tabContainer.selectChild(containerPane);
     return;
    }
   });
  });

  dijit.registry.byClass("dijit.layout.TabContainer").forEach(function( tabContainer ){
   dojo.forEach( tabContainer.getChildren(), function( containerPane ){
    if( dojo.query( containerPane.containerNode ).query( '[name=' + clientId + ']' ).length > 0 ){
     tabContainer.selectChild( containerPane );
    }
   });
  });
 }
}]]></xp:this.value>
 </xp:scriptBlock>
 <xp:repeat id="messageRepeat" styleClass="xspMessage" rows="30" value="#{viewScope.messageObjects}" var="messageObject">
  <xp:this.rendered><![CDATA[#{javascript:return ( viewScope.messageObjects && viewScope.messageObjects.length > 0 ); }]]></xp:this.rendered>
  <xp:this.facets>
   <xp:text xp:key="header" escape="false">
    <xp:this.value><![CDATA[<ul>]]></xp:this.value>
   </xp:text>
   <xp:text xp:key="footer" escape="false">
    <xp:this.value><![CDATA[</ul>]]></xp:this.value>
   </xp:text>
  </xp:this.facets>
  <li>
   <xp:panel rendered="#{!empty(messageObject.clientId)}">
    <a href="#" onclick="return EMessages.setFocus( '#{messageObject.clientId}');">
     <xp:text escape="false">
      <xp:this.value><![CDATA[#{javascript:return (messageObject.label) ? messageObject.label : messageObject.message;
}]]></xp:this.value>
     </xp:text>
    </a>
   </xp:panel>
   <xp:text value="#{messageObject.message}" rendered="#{javascript:return (messageObject.label != '');}" />
  </li>
 </xp:repeat>
</xp:view>

The code should work with fields inside a single level repeat. I'm not sure about deeper nesting. Pop the custom control into the page like you would with the Display Errors control.

Feel free to use the code however you like. If you improve on it, please share with the community.