Reference values

• Allows content of headers and footers to depend on what occurs on that page or previous pages
• Can declare reference values of named types (eg chapter-title, section-title, security-level)
• When creating flow object, can specify value for particular type of reference value
• Value can be sosofo or any other expression language object
• Procedures that search for flow object based on whether the flow object has reference value of some type and on whether areas of flow object fall on the page
• Return generated-object whose kernel is value of reference value