Class MetadataKey

 object --+    
          |    
??.instance --+
              |
             MetadataKey

Known Subclasses:

• MetadataChoicesKey
• , MetadataDependencySpecTreeKey
• , MetadataFSPathIterableKey
• , MetadataFSPathKey
• , MetadataFetchableURISpecTreeKey
• , MetadataKeywordNameIterableKey
• , MetadataLicenseSpecTreeKey
• , MetadataMaintainerIterableKey
• , MetadataPackageIDIterableKey
• , MetadataPackageIDKey
• , MetadataPlainTextSpecTreeKey
• , MetadataRequiredUseSpecTreeKey
• , MetadataSectionKey
• , MetadataSimpleURISpecTreeKey
• , MetadataSlotNameKey
• , MetadataStringIterableKey
• , MetadataStringKey
• , MetadataStringSequenceKey
• , MetadataTimeKey

A MetadataKey is a generic key that contains a particular piece of
information about a PackageID instance.

A basic MetadataKey has:

- A raw name. This is in a repository-defined format designed to closely
  represent the internal name. For example, ebuilds and VDB IDs use
  raw names like 'DESCRIPTION' and 'KEYWORDS', whereas CRAN uses names
  like 'Title' and 'BundleDescription'. The raw name is unique in a
  PackageID.

- A human name. This is the name that should be used when outputting
  normally for a human to read.

- A MetadataKeyType. This is a hint to clients as to whether the key
  should be displayed when outputting information about a package ID.

Subclasses provide additional information, including the 'value' of the
key.