Document the DROID XML mapping

pkg/pronom/internal/mappings/droid.go

@@ -12,30 +12,40 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Package mappings contains struct mappings to unmarshal three
+// Package mappings contains struct mappings to unmarshall three
 // different PRONOM XML formats: the DROID signature file format, the report
 // format, and the container format.
 package mappings
 
 import "encoding/xml"
 
+// Droid Signature File
+
+// Droid describes the basic top-level structure of a DROID signature
+// file.
 type Droid struct {
 	XMLName     xml.Name            `xml:"FFSignatureFile"`
 	Version     int                 `xml:",attr"`
 	Signatures  []InternalSignature `xml:"InternalSignatureCollection>InternalSignature"`
 	FileFormats []FileFormat        `xml:"FileFormatCollection>FileFormat"`
 }
 
+// InternalSignature describes the structure of the InternalSignature
+// section of a DROID signature file.
 type InternalSignature struct {
 	ID            int       `xml:"ID,attr"`
 	ByteSequences []ByteSeq `xml:"ByteSequence"`
 }
 
+// ByteSeq describes the structure of the ByteSequence sections of a
+// DROID signature file.
 type ByteSeq struct {
 	Reference    string        `xml:"Reference,attr"`
 	SubSequences []SubSequence `xml:"SubSequence"`
 }
 
+// SubSequence describes the structure of the SubSequence sections of a
+// DROID signature file.
 type SubSequence struct {
 	Position        int    `xml:",attr"`
 	SubSeqMinOffset string `xml:",attr"` // and empty int values are unmarshalled to 0
@@ -45,13 +55,17 @@ type SubSequence struct {
 	RightFragments  []Fragment `xml:"RightFragment"`
 }
 
+// Fragment describes the structure of the fragment sections of a DROID
+// signature file.
 type Fragment struct {
 	Value     string `xml:",chardata"`
 	MinOffset string `xml:",attr"`
 	MaxOffset string `xml:",attr"`
 	Position  int    `xml:",attr"`
 }
 
+// FileFormat describes the structure of the FileFormat section of a
+// DROID signature file.
 type FileFormat struct {
 	XMLName    xml.Name `xml:"FileFormat"`
 	ID         int      `xml:"ID,attr"`