FIELD RULES

     The field rules define the characteristics of the field. For example,
     whether the field is right justified or left justified. The rules are
     stored for each field individually and the programmer can change any
     or all of the rules as desired.

     There are five different field rules. The interface section of the
     unit includes five byte constants that are used to identify them:

     AllowNull - indicates the user is allowed to leave the field empty,
     i.e. cancels range checking on empty field. Default: On.

     SuppressZero - the field is displayed as blank if the value of a
     (number) field is zero. Default: On.

     RightJustify - the field grows from right to left rather than the
     normal left to right. This is commonly used in financial data entry.
     Default: Off.

     EraseDefault - when the user first enters the field, the default (or
     previous value) is erased if the user strikes a normal alphanumeric
     key. This works in a similar way to the Turbo prompts in the
     integrated environment. Default: Off.

     JumpIfFull - move to the next field to the right if the field is
     filled with data. Default: Off.

     These constants can be summed to combine field rules. For example, a
     field may be defined as having Rules AllowNull+SupressZero. If one of
     the constants is omitted from a field Rules declaration, then that
     rule will not be enacted. For example, a field with Rules
     JumpIfFull+EraseDefault+SupressZero will not be right justified.

     The following procedure can be used to override the default rules:

     In addition to the basic formatting options outlined in the section
     Field Formats (above), the Toolkit provides a facility to restrict
     input to a specific set of characters, or specifically dis-allow
     certain characters.

     For example, the only valid characters for a field that identifies a
     warehouse part number may be "A B C 1 2 3 4 5 6". Alternatively, a
     field that is a filename may allow any alphanumeric character except
     the "*" and "?" characters. Both of these conditions can be
     accommodated.

     Note: it is normal to only specify either allowable characters or
     disallowable characters, not both!

     A constant No_Char can be used to indicate that no characters are
     being set. To define only the field Rules, set both character sets to
     No_Char, e.g.