The dir codec decodes a filesystem directory into a Collection of CreativeWorks. It encodes a Collection as directory, with each CreativeWork by default being encoded using the html codec.
The dir codec is useful for publishing a directory of files (possibly of varying file types) as a directory of HTML (e.g. for publishing documentation).
The main attribute is a boolean indicating if the file is the main file in the directory.
When a directory is decoded, each CreativeWork in the node tree is given a depth on its meta property. This could be used to resolve the root of the tree.
The dir codec encodes a Collection into a file hierarchy with descendent Collections encoded as directories and other types of CreativeWorks encoded as files.
When decoding a node that is a CreativeWork, but not a Collection, the node is wrapped in a new Collection which has the node as its only part. When decoding a node that is not a CreativeWork, the node is wrapped as the only content of a new CreativeWork and then wrapped in a new Collection.
During encoding, a root.json file is created at the top level containing the JSON encoding of the root Collection, including all decendent nodes, but excluding the content property of CreativeWorks. This file is intended to be used as a site map for the generated file tree.