A number of special attributes may be specified on an MXML document, like implements, pageTitle or preloader. These attributes are defined in the flex2.compiler.mxml.builder.DocumentBuilder class. Even if the component does not define properties with these names, the compiler will accept these attributes as valid. The compiler can handle them without setting their values on the component instance.
Special attributes are stored in the specialAttributes2006 and specialAttributes2009 static variables. Which set of special attributes is accepted by the compiler depends on which MXML namespace is specified.
In flex2.compiler.mxml.builder.ComponentBuilder, the super class of DocumentBuilder, has an inner class named ComponentAttributeHandler. These special attributes are passed to its special() method. However, this method does nothing.
DocumentBuilder defines its own inner class named DocumentAttributeHandler. However, this class is never used. Perhaps it was meant to be used and forgotten, or it could be legacy code that was not completely removed. Regadless, the special() method from ComponentAttributeHandler may be overridden in DocumentAttributeHandler. To use DocumentAttributeHandler, set the attributeHandler property of DocumentBuilder to a new instance of DocumentAttributeHandler in the DocumentBuilder constructor after the call to super().
DocumentAttributeHandler already overrides the dynamicProperty() method. However, since DocumentAttributeHandler was not used, it is probably best to remove this override to avoid unintended conflicts.