Previous Next

                                                    688
       CHAPTER 8                                                              Interactive Features



       Beginning with PDF 1.4, the field dictionary for check boxes and radio buttons
       contains an optional Opt entry (see Table 8.76), which holds an array of text
       strings representing the export value of each annotation in the field. It is used for
       the following purposes:

       • To represent the export values of check box and radio button fields in non-Lat-
          in writing systems. Because name objects in the appearance dictionary are lim-
          ited to PDFDocEncoding, they cannot represent non-Latin text.

       • To allow radio buttons or check boxes to be checked independently, even if
          they have the same export value.
          An example is a group of check boxes that are duplicated on more than one
          page, and the desired behavior is that when a user checks a box, the corre-
          sponding boxes on each of the other pages is also checked. In this case, each of
          the corresponding check boxes is a widget in the Kids array of a check box field.
          Note: For radio buttons, the same behavior occurs only if the RadiosInUnison flag
          is set. If it is not set, at most one radio button in a field can be set at a time. See
          implementation note 121 in Appendix H.

               TABLE 8.76 Additional entry specific to check box and radio button fields
KEY   TYPE           VALUE

Opt   array of       (Optional; inheritable; PDF 1.4) An array containing one entry for each widget annota-
      text strings   tion in the Kids array of the radio button or check box field. Each entry is a text string
                     representing the on state of the corresponding widget annotation.
                     When this entry is present, the names used to represent the on state in the AP dictionary
                     of each annotation are computer-generated numbers equivalent to the numerical posi-
                     tion (starting with 0) of the annotation in the Kids array. This allows distinguishing be-
                     tween the annotations even if two or more of them have the same value in the Opt array.
                     For example, two radio buttons may have the same on state, but if the RadiosInUnison
                     flag is not set, only one of them at a time can be checked by the user.


       Radio Buttons

       A radio button field is a set of related buttons. Like check boxes, individual radio
       buttons have two states, on and off. A single radio button may not be turned off
       directly but only as a result of another button being turned on. Typically, a set of
       radio buttons (annotations that are children of a single radio button field) have at

Previous Next