LatticeXvl was an experimental parametric geometry approach that was not adopted into the X3D standard.
These nodes nevertheless demonstrate extensibility techniques for integrating new capabilities using X3D DOCTYPE (DTD).
The Xvl nodes are merely experimental: not approved by the X3D Abstract Specification, not in the X3D XML Schema, and not in the X3D Unified Object Model (X3DUOM).
The LatticeXvl examples
do show how
was integratable as a commercial extension within X3D.
This technique is repeatable.
The extension approach to XML DTD validation has been maintained through each version of X3D,
and is documented further in the actual
X3D DTDs and Schemas.