Hello Milena

Using a plain textbox is out of the question.
It delivers a poor user experience when the field has to comply to a certain regex.

While a mask (without the maxlength attribute) does prevent users from entering something that doesn't meet our regex pattern and length requirements, nothing prevents someone from posting their own data to our endpoint without using our frontend.

It's also best practice to validate data as early as possible in MVC, before it even hits the data access layer.
People on stackoverflow would downvote you into oblivion if you were to say that validation attributes aren't needed and can be omitted.

My gut feeling is that the "bug" you fixed in the wrappers wasn't a bug at all but intended behavior, since it did render before, but in another telerik-only html attribute so the control itself could do it's own length checking and not rely on built in browser features.
I fail to see any reason why anyone would put a higher maxlength requirement on their properties than their mask's length. Doing that kind of defeats the purpose of the mask in the first place. You'd be contradicting yourself when you'd say "Oh, my field needs to have a length of 5 and can only contain numbers" and then put a length validation on it that's greater than 5. Let's say for argument sake you were to use a maskedtextbox to enter localized phone numbers. Atleast 1 mask would have the same length as your database field (and thus validation attribute) in that case, while other masks may be smaller. The textbox would stop working at that point.

I'm fine with the input having the new maxlength reinforcement, but then the maskedtextbox itself should be able to process your inputs correctly and not plain stop working when you throw the most basic example at it. 
No user is going to want to type their text somewhere and then copy-paste that value inside the maskedtextbox after first having to select everything that's currently inside that textbox. Our users would skin me alive if I were to ask that of them.

Regards

Hello Milena

Just so we're clear, you're saying that the fact that the MaskedTextBox straight up doesn't work anymore as soon as you use a MaxLength attribute on your property is intended behaviour?

Please give us an example on how we should use this "new intended functionality" then, because the only way we're getting this to work again is by straight up removing our validation attributes...

We're using the TextBox for data that always has a certain length and shape, so our mask's length will always be as long as our StringLength's min/max length.

Regards

Hello Milena

While this may be true for the jquery version of the library, it is (partially) incorrect for the core MVC version.
This is the HTML it generates for the 2022.2.802 version of the library:

<span class="k-input k-maskedtextbox k-input-solid k-input-sm k-rounded-md" style="width: 100%;">
    <input data-val="true" data-val-length="Aangiftenummer mag maximaal 16 karakters bevatten!" data-val-length-max="16" data-val-regex="Aangiftenummer moet formaat xxx-xxxxxxx-xx-x hebben!" data-val-regex-pattern="^([0-9a-zA-Z]){3}-([0-9a-zA-Z]){7}-([0-9a-zA-Z]){2}-([0-9a-zA-Z]){1}$" id="WharfNotificationDetails_RszDeclarationNumber" maxlength="16" name="WharfNotificationDetails_RszDeclarationNumber" style="width:100%;" type="text" value="" data-role="maskedtextbox" class="k-input-inner" autocomplete="off" aria-placeholder="AAA-AAAAAAA-AA-A">
    <span class="k-input-validation-icon k-icon k-i-warning k-hidden"></span>
</span>

<span class="k-input k-maskedtextbox k-input-solid k-input-sm k-rounded-md k-valid" style="width: 100%;">
    <input data-val="true" data-val-length="Aangiftenummer mag maximaal 16 karakters bevatten!" data-val-length-max="16" data-val-regex="Aangiftenummer moet formaat xxx-xxxxxxx-xx-x hebben!" data-val-regex-pattern="^([0-9a-zA-Z]){3}-([0-9a-zA-Z]){7}-([0-9a-zA-Z]){2}-([0-9a-zA-Z]){1}$" id="WharfNotificationDetails_RszDeclarationNumber" name="WharfNotificationDetails_RszDeclarationNumber" style="width:100%;" type="text" value="" data-role="maskedtextbox" class="k-input-inner" autocomplete="off" aria-placeholder="AAA-AAAAAAA-AA-A">
    <span class="k-input-validation-icon k-icon k-i-warning k-hidden"></span>
</span>

@(Html.Kendo().MaskedTextBoxFor(m => m.WharfNotificationDetails_RszDeclarationNumber)
.Size(ComponentSize.Small)
.Mask("AAA-AAAAAAA-AA-A")
.HtmlAttributes(new { style = "width:100%;" })
)

public class WharfNotificationDetails {
        [Display(Name = "Aangiftenummer")]
        [StringLength(16, ErrorMessage = "Aangiftenummer mag maximaal 16 karakters bevatten!")]
        [RegularExpression(@"^([0-9a-zA-Z]){3}-([0-9a-zA-Z]){7}-([0-9a-zA-Z]){2}-([0-9a-zA-Z]){1}$", ErrorMessage = "Aangiftenummer moet formaat xxx-xxxxxxx-xx-x hebben!")]
        public string WharfNotificationDetails_RszDeclarationNumber { get; set; }
}

Regards