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. Tinderbox can open multiple TBX documents at once - limited only by the host computers resources.
Any non-default doc-level preferences 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.