In the left panel a tree is used to display schema
in a hierarchical format. All elements of complex type is corresponding
to a container node. The elements of simple type and attributes are
leaf nodes. Users can quickly browse the hierarchical elements and
access detailed information for an element/attribute by highlighting the
corresponding tree node in the tree.
When a tree node is cliked on the left frame,
all its attributes and their constraints are shown in the right panel.