Adobe Acrobat SDK
Interactive Features (Chapter 8 in PDF Reference)
Adobe® Supplement to the ISO 32000
8.2.4 Collections 33
New values for the
ID
key shall be obtained by a conforming reader by accessing the
Free
entry in the
root folder. If an
ID
value is used from the
Free
entry array, the array is updated.
As previously described, the
Name
entry is a file name for a folder. A folder, as well as its associated files,
have naming restrictions inherited from the
Universal Container Format (UCF)
specification. (See the
Bibliography
.) Strings that conform to these restrictions are known as
file names
. A valid file name
conforms to the following requirements:
●
The string shall be a PDF text string.
●
The string shall not contain any embedded NULL characters.
●
The number of characters in the string shall be between 1 and 255 inclusive.
●
The string shall not contain any of the eight special characters: U+002F SOLIDUS (/), U+005C REVERSE
SOLIDUS (\), U+003A COLON (:), U+002A ASTERISK (*), U+0022 QUOTATION MARK ("), U+003C
LESS-THAN SIGN (<), U+003E GREATER-THAN SIGN (>), and U+007C VERTICAL LINE (|).
●
The last character shall not be a U+002E FULL STOP (.).
A conforming reader may choose to support invalid names or not. If not, an appropriate error message
shall be provided.
In addition to the restriction on naming folders, as just described, it is further required that two file names
in the same folder do not map to the same string following case normalization. Two file names that differ
only in case are disallowed within the same folder. See http://www.unicode.org/reports/tr21/tr21-5.html
for information on case normalization.
The
CI
entry (a collection item dictionary) allows user-defined metadata to be associated with a folder,
just as it does for embedded files in a collection.
Folders are indirect objects, and relationships between folders in the tree are specified using
Parent
,
Child
, and
Next
keys.
When folders are used, all files in the
EmbeddedFiles
name tree (see Table 3.28 of the
PDF Reference
)
shall be treated as members of the folder structure by a conforming reader. The association between files
and folders is accomplished using a special naming convention on the key strings of the name tree. See
the
PDF Reference
, Section 3.8.5, “Name Trees,” for a discussion of the key strings. If no folder structure is
specified, conforming readers show all files in the collection in a flat list, maintaining compatibility with
older viewers.
Thumb
stream
(
Optional; ExtensionLevel 3
) A stream object defining the thumbnail
image for the folder
See Section 8.2.3, “Thumbnail Images” of the
PDF Reference
.
Free
array
(
Optional; only used by root folder; ExtensionLevel 3
) An array
containing
ID
values that are not currently in use by the folder
structure. The array contains zero or more pairs of numbers, a low
value followed by a high value. Each pair represents an
endpoint-inclusive range of values that are available for use when
a new folder is added. Each low value is less than or equal to its
corresponding high value.
TABLE 8.6c Entries in a folder dictionary
KEY
TYPE
VALUE
