A Tinderbox document is a saved as a single file, with a '.tbx' extension - and thus are often referred to as 'TBX' documents.
Tinderbox can create and save multiple TBX documents - limited only by storage space available - and can open multiple TBX documents at once - limited only by the host computers resources. When Tinderbox is started, it will open any documents open when the app was last closed.
Tinderbox also tracks recently opened documents on a sub-menu of the File menu. If multiple documents are open, the application's Window menu list all open windows from all documents. Note that the latter listing does not indicate the document to which each document belongs
Any non-default Document Settings and other customisations (links types, colours, attributes, etc.) are stored in the TBX.
A TBX stores its data in XML format; for some users with XML skills this can provide another way to interface with, or view the data. Users altering TBX documents by editing the XML source should not this is not formally supported as an editing method - i.e. don't expect Tech Support to clear up after user mistakes. See more on the XML structure of TBX documents.