Every HTML input on a form must have a unique ID. The -ID parameter is used with the $Input command to specify the ID that will be generated for that input. This ID can be used for styling via CSS. This ID is also referenced within form actions using the syntax $Form -id'xx'$, which the ID from the input is specified in the form action.
Example: Specify an ID for first name
Form Body Text: $input -firstname -id'first_name'$
Rendered HTML: <input id="first_name" name="first_name" type="text" value="" class="text" />
