This one seems to be documented here: https://bugs.adobe.com/jira/browse/ASC-2800

Consider the following:

for each (var element : XML in _samplePresetsXml.children())
{
    var ns : Namespace = new Namespace(element.namespace());
    default xml namespace = ns;
    ….

line with "default xml…" throws the following error during launch:

VerifyError: Error #1025: An invalid register 2 was accessed.
      at PresetsConfiguration/_PresetsConfiguration_XML1_i()
      at PresetsConfiguration()[D:\Work\Flex3\PresetsConfiguration\PresetsConfiguration.mxml:114]
      at _PresetsConfiguration_mx_managers_SystemManager/create()
      at mx.managers::SystemManager/initializeTopLevelWindow()[E:\dev\flex_3_beta2sdk\frameworks\projects\framework\src\mx\managers\SystemManager.as:2428]
      at mx.managers::SystemManager/docFrameHandler()[E:\dev\flex_3_beta2sdk\frameworks\projects\framework\src\mx\managers\SystemManager.as:2320]

While the following two variants work completely fine:

var ns : Namespace = new Namespace(_samplePresetsXml.namespace());
for each (var element : XML in _samplePresetsXml.children())
{
    ns = new Namespace(element.namespace());
    default xml namespace = ns;
    …

OR

var ns : Namespace = new Namespace(_samplePresetsXml.namespace());
for each (var element : XML in _samplePresetsXml.children())
{
    default xml namespace = ns;
    …

My XML is pretty straightfoward:

<?xml version="1.0" standalone="yes"?>
<Examples xmlns=http://tempuri.org/Examples.xsd>
  <Example>
    <Id>17d4d7f6-d7d4-4de4-b8b9-e04a5ea5d35b</Id>
    ….

A piece of advice: when working with XML, get to know namespaces and what role they play in retrieving node values. In reference to above, this is how you would get to GUID in ID if not using "default xml namespace" directive:

trace(">>" + element.ns::Id.text());

Mike Grushin
CTO

We are playing around with Flex Builder 3 and I ran into a few issues that I wanted to document:

————————————————————————

<mx:Label x="62" y="75" text="Label" width="517" height="353" id="_label"/>

You cannot user "_label" or "label" as id of <mx:Label>. Flex gives the following errors

_label: Attempting to initialize non-public inherited property ‘_label’ from MXML
label: Attempting to initialize inherited property ‘label’ of type ‘String’ with value of incompatible type ‘mx.controls.Label’.

————————————————————————

Consider the following simple application.

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" applicationComplete="ApplicationComplete()">
      <mx:Script>
            <![CDATA[
                  private function ApplicationComplete() : void
                  {
                        _presetsTextArea.text = "Test";
                  }
            ]]>
      </mx:Script>
      <mx:TabNavigator bottom="9" right="9" left="10" top="10">
            <mx:Canvas label="Visual" width="100%" height="100%">
            </mx:Canvas>

            <mx:Canvas label="Source" width="100%" height="100%">
                  <mx:TextArea id="_presetsTextArea" right="10" bottom="37" left="10" top="10"/>
                  <mx:Button x="810" y="665" label="Apply"/>
            </mx:Canvas>
      </mx:TabNavigator>
</mx:Application>

The following line produces a runtime error:

_presetsTextArea.text = "Test";

Error:

Cannot access a property or method of a null object reference.

Works fine if TexInput is in the first "tab". After some debugging it looks like immediate children of TabNavigator are added to stage, but canvas children are added only when user clicks on the appropriate tab. Not the behavior I expected.

————————————————————————

You have to be careful which part of Flex Builder is focused when you press Ctrl-Z:

1. Add new file/class
2. Start typing code
3. Click outside of code editing window (console, project treeview, etc)
4. Press Ctrl-Z
5. Your new file is removed together with the work you’ve done
6. If you think it is in the Recycle Bin — you are wrong!
7. Redo also doesn’t work

Mike Grushin
CTO