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                                          683
SECTION 8.6                                                            Interactive Forms



Rich text strings are specified by the RV entry of variable text form field dictionar-
ies (see Table 8.71) and the RC entry of markup annotation dictionaries (see Table
8.21). Rich text strings may be packaged as text streams (see Section 3.8.2, “Text
Streams”). Form fields using rich text streams should also have the RichText flag
set (see Table 8.77).

A default style string is specified by the DS entry for free text annotations (see Ta-
ble 8.25) or variable text form fields (see Table 8.71). This string specifies the de-
fault values for style attributes, which are used for any style attributes that are not
explicitly specified for the annotation or field. All attributes listed in Table 8.74
are legal in the default style string. This string, in addition to the RV or RC entry, is
used to generate the appearance. The following entries are ignored by PDF 1.5-
compliant viewers: the Contents entry for annotations, the DA entry for free text
annotations, and the V, DA, and Q entries for form fields.

Note: Markup annotations other than free text annotations (see “Markup Annota-
tions” on page 616) do not use a default style string because their appearances are
implemented using platform controls requiring the viewer application to pick an ap-
propriate system font for display.

When a form field or annotation contains rich text strings, the flat text (character
data) of the string should also be preserved (in the V entry for form fields and the
Contents entry for annotations). This enables older viewer applications to read
and edit the data (although with loss of formatting information). The DA entry
should be written out as well when the file is saved.

If a document containing rich text strings is edited in a viewer that does not sup-
port PDF 1.5, the rich text strings remain unchanged (because they are unknown
to the viewer), even though the corresponding flat text may have changed. When
a viewer that supports PDF 1.5 reads a rich text string from a document, it must
check whether the corresponding flat text has changed by using the following
procedure:

1. Create a new flat text string containing the character data from the rich text
   string. Character references (such as 
) should be converted to their char-
   acter equivalents.
  Note: No attempt should be made to preserve formatting specified with markup
  elements. For example, although the <p> element implies a new line, a carriage
  return should not be generated in the associated flat text.

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