Motivation

• If several shapes have the same geometry or appearance, you must use multiple duplicate nodes, one for each use
• Instead, define a name for the first occurrence of a node
• Later, use that name to share the same node in a new context

Syntax: DEF

The DEF syntax gives a name to a node.

Using DEF

• DEF must be in upper-case
• You can name any node
• Names can be most any sequence of letters and numbers
  • Names must be unique within a file

Syntax: USE

The USE syntax uses a previously named node

Using USE

• USE must be in upper-case
• A re-use of a named node is called an instance
• A named node can have any number of instances
  • Each instance shares the same node description
  • You can only instance names defined in the same file

Using named nodes

Naming and using nodes:

• Saves typing
• Reduces file size
• Enables rapid changes to shapes with the same attributes
• Speeds browser processing

Names are also necessary for animation ...

A sample use of node names

Summary

• DEF names a node
• USE uses a named node