The value of this attribute is an NSNumber object containing integer specifying NSStringEncoding for the file; default for plain text is the default encoding. This key in options can specify the string encoding for reading the data. Upon return, the document attributes can contain the actual encoding used. For writing methods, this value is used for generating the plain text data.
The value of this attribute is an NSNumber object containing a float. For RTF files only, stores the version of Cocoa with which the file was created. Absence of this value indicates RTF file not created by Cocoa or its predecessors.
The value of this attribute is an NSString object indicating which document type was used to interpret the document, specified as a UTI; for reading, this is available along with NSDocumentTypeDocumentAttribute, but for writing the two are mutually exclusive.