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                                               677
SECTION 8.6                                                         Interactive Forms



ancestors. For a field with no parent, the partial and fully qualified names are the
same. For a field that is the child of another field, the fully qualified name is
formed by appending the child field’s partial name to the parent’s fully qualified
name, separated by a period ( . ):

   parent’s_full_name . child’s_partial_name

For example, if a field with the partial field name PersonalData has a child whose
partial name is Address, which in turn has a child with the partial name ZipCode,
the fully qualified name of this last field is

   PersonalData . Address . ZipCode

Thus, all fields descended from a common ancestor share the ancestor’s fully
qualified field name as a common prefix in their own fully qualified names.

It is possible for different field dictionaries to have the same fully qualified field
name if they are descendants of a common ancestor with that name and have no
partial field names (T entries) of their own. Such field dictionaries are different
representations of the same underlying field; they should differ only in properties
that specify their visual appearance. In particular, field dictionaries with the same
fully qualified field name must have the same field type (FT), value (V), and de-
fault value (DV).


Variable Text

When the contents and properties of a field are known in advance, its visual ap-
pearance can be specified by an appearance stream defined in the PDF file (see
Section 8.4.4, “Appearance Streams,” and “Widget Annotations” on page 640). In
some cases, however, the field may contain text whose value is not known until
viewing time. Examples include text fields to be filled in with text typed by the
user from the keyboard and scrollable list boxes whose contents are determined
interactively at the time the document is displayed.

In such cases, the PDF document cannot provide a statically defined appearance
stream for displaying the field. Instead, the viewer application must construct an
appearance stream dynamically at viewing time. The dictionary entries shown in
Table 8.71 provide general information about the field’s appearance that can be
combined with the specific text it contains to construct an appearance stream.

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