Allow invalid "default values" for exposed fields in availability search

When I developed the Views filter handler for availability I did not understand why there is so few validation in the default supplied filters (numeric and date which I originally extended). With this example, I start to understand why one would not validate values entered in the Views UI for exposed filters. But still, if the user leaves this value untouched, it will lead to a validation error when (s)he presses "Search Availability". (The date filter does not give a validation error but happily converts it to 0 and builds a query with that as value...)

For another site where the client also wanted in-field labels, I used the jQuery defaultvalue plugin. It is easy to use and works like a charm (but this was not a Drupal site). Bonus is that the default values are not sent to the server on submit. Thus no validation errors, no people with "phone" as telephone number...

I think that this is not something this module should provide, but that you should build yourself using the mentioned jQuery plugin. Might be a good candidate for a contrib module ...

I'll see what I can do within the limits of Views and Drupal form handling. Assigning to myself as to create a todo list for 7.x-3.3.

I loosened the validation and it now works. But if you use the date popup module, a date field with an invalid default value will be emptied by that module...