Represents a connection for exchanging file data with another application.
TODO: this page is incomplete.
<doc:transfer onOpen=... onClose=...> creates a transfer tag instance, to be used with requestTransfer.Not used.
A transfer tag instance stands for one connection between two applications. It is created by the requesting application and passed to requestTransfer, or arrives through a transferAbility tag when another application asks to connect.
The .open operator, with an access mode, starts a transfer in that direction, for example <doc.open {w}>; .close ends it. The same connection can be opened and closed more than once.