Form Usability: Validations vs Warnings (Jamie Appleseed)

There’s a major difference between form validations and warnings. Form validations enforce a set of rules and won’t allow the user to proceed, while warnings alert the user about possible problems but will allow them to proceed. While e-commerce sites would do well in adopting both strategies, it’s unfortunately few that make use of warnings (our checkout benchmark study found that 64% don’t have ‘address warnings’), and similarly regrettable we often observe sites enforcing overly restrictive form validations that completely block a (small) sub-group from completing their purchase. (baymard.com)