The option to allow multiple values is used with discrete values and range values. For discrete values, the user can enter multiple single values and they are each treated individually. For range values, the user can enter multiple sets of ranges and each range is treated separately from the other ranges entered. A parameter can also have a collection of both discrete values and range values.

Boolean parameters can be thought of as being similar to checkboxes or option buttons. With checkboxes, each value is independent of the other. That is, selecting or changing one checkbox has no effect on other checkboxes. This is the default behavior of Boolean parameters. Option buttons are used in groups and each is mutually exclusive of the other. Selecting one will automatically turn off all others in the same group. The Place in Parameter Group option lets you place a Boolean parameter in a parameter group. Give it a group number and set whether the parameters in that group are mutually exclusive to each other. If the parameters are mutually exclusive, only one Boolean parameter can be assigned to True at a time. If the user sets two or more parameters to True, only the most recent will keep its value; the others are reset to False.

The Create Parameter Field dialog box for Boolean data types has different options. When you change the Value Type property to Boolean, the lower half of the dialog box changes to reflect the new options (see Figure 5-3).

Figure 5-3. The Create Parameter Field dialog box for Boolean data.