The Invalid Value option is intended to prohibit users from selecting options like this one:
When you save your file the first time after adding a Spry Validation Select widget, Dreamweaver will notify you of the supporting files: SpryValidationSelect.css and SpryValidationSelect.js. Depending on your Property inspector settings, the Spry Validation Select widget provides up to four different states: n Initial: The default state of the text field. n Required: Displays an error message if the Blank Value option has been selected and no choice has been made. NOTE NOTE 620 Adding Advanced Design Features Part III n Invalid: Displays an error message if the Invalid Value option has been selected and the user has selected an entry with the designated improper value. n Valid: Shown when the entry has passed validation. As with the other form validation widgets, you switch from one state to another by selecting a different entry from the Preview States list in the Property inspector. This action exposes the possible error messages and CSS stylings for each state so you can modify them if desired. Spry Validation Checkbox The Spry Validation Checkbox can be used with a single checkbox if it is required or with multiple checkboxes to control the number selected.