public ModelSource(Lookup lookup,
Create a model source object given the lookup context. If editable is false
the model cannot be mutated. Note that editable is static attribute of the
model source, and does not reflect the access attribute of the associated file.
lookup - Lookup object associated with this ModelSource. Lookup minimally
contains a File path of the backing file of the model and a javax.swing.text.Document object.
editable - whether the model is supposed to be mutated.
Returns the lookup object associated with this ModelSource. Lookup minimally
contains a File absolute path or FileObject of the backing file of the model
and javax.swing.text.Document object. If model is DOM, the lookup should
also contains javax.xml.transform.Source object for use in cases of relative
resolution of resource such as validation.