Proposal : New XML node instance syntax

[kwokcb]

Prototype

This code prototypes an "additive" approach to introducing this new syntax as described in issue #2984.

Properties

• XML write option allows either current or proposed syntax. Default is current.
• XML read handles both syntax variants
• This allows moving back and forth between either formats.
• On next version "upgrade", all current libraries can be converted to new syntax and write option defaults to new syntax.

Examples

• Modify graph editor to write new syntax
• Modify mxformat.py utility to write either syntax. i.e. supports bidirectional conversion.
  • Tested converting all libraries and resources using this to new syntax and re-ran tests without failure.

[jstone-lucasfilm]

@kwokcb This is a very interesting proposal that demands significant thought and discussion from the MaterialX community, but I'll provide one initial suggestion:

Since you are proposing a brand new syntax in MaterialX, perhaps the best starting point is a PR for new text in the Specification Proposals document, rather than a PR for an implementation in the codebase?