The syntax of an MXML document is now represented by a set of thread-safe read-only interfaces (IMXMLData, IMXMLTagData, IMXMLTagAttributeData, etc.) Clients of the MXML document, such as the MXML tree builder, now access the document only through these interfaces and no longer use the concrete classes. This makes the syntax view (i.e., IMXMLData) similar to the semantic view (i.e., IMXMLFileNode).
Next I'll polish the API of these interfaces a bit (probably removing the "Data", which doesn't add anything useful), separate the interfaces and the classes into separate packages, and write unit tests to verify that we're creating the correct IMXMLData structure, at least in the case of well-formed MXML. I should have done this before writing the AST tests, because syntactically parsing the MXML precedes constructing the tree. - Gordon
