The last characteristic of the structure chart is to determine the manner in which accelerator keys operate. An accelerator key for a form field is defined by an underlined character in some label text. For example, the text associated with a check box normally has one character underlined. Next to an entry field, there is usually a label field which identifies it. An accelerator key is defined as the Alt key plus one of the underlined characters, and when pressed, is supposed to shift the input focus to a specific field. However, one is faced with the problem that in dense forms, it is not always easy (or even preferable), to select unique underlined characters for each field. Also, entry fields (for example), have no associated text to underline. Hence, the structure chart again comes into play.
You cannot experiment with the following in layout mode, but you can in test mode and in the painter's own dialogs. Accelerator keys work as follows.
When an accelerator key is pressed (i.e. the Alt key plus an underlined character), the input focus moves in tab sequence order from the current form field to the first available form field which either is, or is after the form field whose underlined character matches the one pressed. Thus to move to an entry field which has an associated label with an underlined character, locate the label field immediately higher than the entry field in the structure chart. Pressing Alt plus the underlined character from the label moves the focus to the entry field, because the label field is not available, and the entry field immediately follows it in tab sequence order. If the same underlined character appears in multiple form fields, successively pressing Alt plus that character moves the input focus to each field in turn.
When choosing obvious accelerator characters becomes difficult because of the density of a form, use the following approach. Ensure that all frames at the same level have good and unique choices for underlined characters. This enables the keyboard user to at least get to any particular frame immediately. Within the frame, you can then re-use accelerator characters that appear in fields within other frames.