client side validation can be accomplished in a few ways:
1) Use Dreamweaver Spry Validation
2) Use the Client validation of CSS Form Builder.
you can convert existing form elements to Spry Elements by selecting them in Design view, then go to Insert -> Spry -> and selecting the correct Spry Validation element type.
once converted to a spry validation element, select it in design view, then click the blue bounding box to open the Spry Validation editor in the property inspector to configure the validation trigger and data types.
for CSS Form builder client validation, go to Webassist -> Forms -> Validation -> Client validation to open the client validation wizard.
to remember enter form data when server validation fails, select each form element in design view, then in the property inspector, click the lightning bolt next to Initial value and select the corresponding binding from the Validated entries binding group.