This operation is performed by the
“common.app_tree” Tree: for every Node of the
tree, an “object” XML element is generated, with the
following attributes: name, class, base (class). Each object contains an
element for each Property (generated by the
“write” method of Property) and
then an “object” element for all its sub-widgets and/or
sizers. Properties in the “sizer_properties”
dictionary are treated in a different way, as well as the children of a
sizer, which are sub-elements of “sizeritem”
objects: see the source code for details.