Variable

This is a placeholder for the <xforms:variable> feature.

Closely allied with AVT

Erik's notes:

eXforms proposal: http://exforms.org/variable.html
Orbeon implementation: http://wiki.orbeon.com/forms/doc/developer-guide/xforms-variables
could also prefer the shorter <var> tag name, especially if we go with a @value attribute instead of a @select attribute

Proposal

You can define variables everywhere outside xf:model, as a child of model or as as child of an xforms action (even if it is in the model)
- Scoping:
  - A given variable is visible to any XPath expression on a following sibling element or on a following sibling element's descendant element.
  - Model variables are also visible from XPath expression outside of models whenever that model is in scope.
Binds automatically create variables with their id as name of the variable -> Sounds really handy, but not yet sure where the variables should be available