An MXF file is structured as a contiguous list of Key, Length Value items (KLV). The Key gives the meaning of the item, and the value is the data contained within the item.
This data may itself be another list of KLV items, and each of the contained items may be another set of KLV items and so on.
This view reports on the structure of the file also optionally showing the details within partitions in the file. Viewing the partition information is selected in the preferences dialog, but is off by default.
More information on the tests performed are documented in full on the reference page