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                                                 184
       CHAPTER 3                                                                           Syntax



KEY    TYPE          VALUE

EF     dictionary    (Required if RF is present; PDF 1.3; amended to include the UF key in PDF 1.7) A dictio-
                     nary containing a subset of the keys F, UF, DOS, Mac, and Unix, corresponding to the
                     entries by those names in the file specification dictionary. The value of each such key
                     is an embedded file stream (see Section 3.10.3, “Embedded File Streams”) containing
                     the corresponding file. If this entry is present, the Type entry is required and the file
                     specification dictionary must be indirectly referenced. (See implementation note 46
                     in Appendix H.)
                     Note: It is recommended that the F and UF entries be used in place of the DOS, Mac, or
                     Unix entries.

RF     dictionary    (Optional; PDF 1.3) A dictionary with the same structure as the EF dictionary, which
                     must also be present. Each key in the RF dictionary must also be present in the EF dic-
                     tionary. Each value is a related files array (see “Related Files Arrays” on page 186)
                     identifying files that are related to the corresponding file in the EF dictionary. If this
                     entry is present, the Type entry is required and the file specification dictionary must
                     be indirectly referenced.

Desc   text string   (Optional; PDF 1.6) Descriptive text associated with the file specification. It is used
                     for files in the EmbeddedFiles name tree (see Section 3.6.3, “Name Dictionary”).

CI     dictionary    (Optional; must be indirect reference; PDF 1.7) A collection item dictionary, which is
                     used to create the user interface for portable collections (see Section 3.10.5, “Collec-
                     tion Items).


3.10.3 Embedded File Streams

       File specifications ordinarily refer to files external to the PDF file in which they
       occur. When a PDF file is archived or transmitted, all external files it refers to
       must accompany it to preserve the file’s integrity. Embedded file streams (PDF 1.3)
       address this problem by allowing the contents of referenced files to be embedded
       directly within the body of the PDF file. For example, if the file contains OPI
       (Open Prepress Interface) dictionaries that refer to externally stored high-
       resolution images (see Section 10.10.6, “Open Prepress Interface (OPI)”), the
       image data can be incorporated into the PDF file with embedded file streams.
       This makes the PDF file a self-contained unit that can be stored or transmitted as
       a single entity. (The embedded files are included purely for convenience and need
       not be directly processed by any PDF consumer application.)

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