I dont care much if they enter an invalid date like .
As long as it is in that format so my php can read it and not produce an error.
In many cases, the values you need are some other data types, like integers or dates.
Therefore, you also have to make sure that the values that users enter can be correctly converted to the appropriate data types.
A disadvantage of this approach is that users don't know that they've made an error until after they submit the page.