Widget Child Change History
===========================
3.5.0
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* No changes.
3.4.1
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* No changes.
3.4.0
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* No changes
3.3.0
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* Changed instanceof to Y.instanceOf, to prevent leaks in IE7
3.2.0
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* No changes
3.1.1
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* No changes
3.1.0
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* Add new ROOT_TYPE property to constrain the behavior of the "root" attribute
to instances of a specified type
* Fixes to remove method so that it always returns a reference to the
child removed