Looking at the one line summary for `tabbed`, it seems that `tabbed` provides an `xid` of a window into which an xembed-aware application can be placed.
Reading the man page for `xterm` I can see the `-info windowID` option, which is explained as « _Given an X window identifier (an integer, which can be hexadecimal, octal or decimal according to whether it begins with "0x", "0" or neither), xterm will reparent its top-level shell widget to that window. This is used to embed xterm within other applications._ »
I would suggest, therefore, that if `tabbed` provides a number such as `0x320005` and you were to run `xterm -into 0x320005`, you'd find the `xterm` running inside the window provided by `tabbed`.
The bottom line, though, is that unless your target application supports XEmbed you're not likely to have a lot of use for `tabbed`.
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_Disclaimer: I don't have`tabbed` installed._