Add database_specific to affected[].ranges[].

This is intended only for metadata that enables databases to losslessly
convert OSV entries back into their original representation.

Part of #35.

docs/schema.md

@@ -82,7 +82,8 @@ A JSON Schema for validation is also available
 				"introduced": string,
 				"fixed": string,
 				"limit": string
-			} ]
+			} ],
+			"database_specific": { see description }
 		} ],
 		"versions": [ string ],
 		"ecosystem_specific": { see description },
@@ -483,6 +484,17 @@ describing a single range.  The range object defines the fields `type`,
 
 This field is required if `affected[].ranges[].type` is `GIT`.
 
+### affected[].ranges[].database_specific field
+
+The `ranges` object's `database_specific` field is a JSON object holding
+additional information about the range from which the record was obtained. The
+meaning of the values within the object is entirely defined by the database and
+beyond the scope of this document.
+
+Databases should only use this field to enable lossless conversion from the OSV
+format back into the original database representation. Values in this field
+have no effect on the [evaluation algorithm](#evaluation).
+
 ### affected[].ecosystem_specific field
 
 The `affected` object's `ecosystem_specific` field is a JSON object holding

validation/schema.json

@@ -146,6 +146,9 @@
                     ]
                   },
                   "minItems": 1
+                },
+                "database_specific": {
+                  "type": "object"
                 }
               },
               "allOf": [