The entire sketch in Base64 encoded binary format.
Data is a specially formatted property that is not human readable. It is for reading and writing sketches.
The Data property gets and sets the entire sketch image. It is used for saving and loading sketches in their native format, thereby preserving the various objects and layers contained therein. Get this property to write a sketch to the database, then later set this property with previously saved data.
Note that the format of the data is base64 encoded binary, which ensures that it will never contain unusual characters or delimiters. This makes it simple to save a sketch anywhere in the database, whether it be in its own standalone record or within a multivalued field of a much larger one.