Values to specify zettel parts

When working with zettel, you could work with the whole zettel, with its metadata, or with its content:

zettel: Specifies that you work with a zettel as a whole. Contains identifier, metadata, and content of a zettel.
meta: Specifies that you only want to cope with the metadata of a zettel. Contains identifier and metadata of a zettel.
content: Specifies that you are only interested in the zettel content. Contains identifier and content of a zettel.