I'd like to define a single instance of a text variable and have it available to all documents in a Book (.indb). Can't figure out how. Is this possible?
InDesign CS5.5 (both mac & pc versions)
InDesign can't, automatically.
But it is an option in the Book panel -- you can enable text variables to synchronize along with loads of other stuff. Then all it needs is a quick click on the Synchronize button.
Just make sure you only enable the items you really want to sync.
Text Variables can by synchronized in a Book file, just like Paragraph Styles, Swatches, etc. It's available in Synchronize Options from the book panel menu.