The PCAPng structure viewer
When selecting a single PCAPng trace file in the file list TraceWrangler will show an additional tab on the lower right pane, containing file format details. This can be helpful if you want to know what kind of sections and blocks a trace file contains, so if you're developing your own PCAPng code you can use TraceWrangler to verify your written files. Of course, this tab will only be shown for PCAPng files.
This screen shot shows an example: