Support for validation concerns on action fields

[sazzer]

I know a lot of this can be done with classes, but it seems to me it would be a good improvement to have a standard set of validation constraints defined as standard on the fields in an action. For example, stating that a field is required, or read-only, or that it must have a certain max or min length.

From the example in the readme, for example, we might have:

        { "name": "orderNumber", "type": "hidden", "value": "42", "required": true, "readOnly": true },
        { "name": "productCode", "type": "text", "required": true, "minLength": 5, "maxLength": 50 },
        { "name": "quantity", "type": "number", "required": true, "min": 1, "max": 100 }

Clients can then have a much better understanding of how the fields need to work, which can give a much better user experience.

The set defined in HAL Forms would seem to be a decent starting point, though the way that options works there is quite complicated to handle.

Cheers