L.5.4 ShapeType Element
The ShapeType element defines a definition, or template, for a shape. Such a template is “instantiated” by creating a Shape element that references the ShapeType. The shape can override any value specified by its ShapeType, or define attributes and elements the ShapeType does not provide. A ShapeType cannot reference another ShapeType.
The attributes and elements a ShapeType uses are identical to those of the Shape element, with these exceptions.
CSS positioning attributes are ignored and not passed to individual Shape instances.
Visibility is always hidden.
A VML authoring agent can make the ShapeType visible, in which case the CSS positioning attributes are meaningful.
The ShapeType element is used to define a shape once and reference it multiple times throughout a document. One of the most useful attributes or elements a ShapeType defines is a complex Path. Since Path coordinates are defined in a relative coordinate space that scales with a shape’s height and width, this is very flexible for defining a shape outline that can be custom scaled and formatted for a given use.