Implement "get element target" and "get element noopener" algorithms

[jdm]

Spec:

• https://html.spec.whatwg.org/multipage/semantics.html#get-an-element's-target
• https://html.spec.whatwg.org/multipage/links.html#get-an-element's-noopener

We'll want to replace the places in the code that do these in an ad-hoc fashion, like this and this and ensure we're following the relevant spec steps in https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#form-submission-algorithm:get-an-element's-noopener and https://html.spec.whatwg.org/multipage/links.html#following-hyperlinks:get-an-element's-target.

[avr1254]

@highfive I'll take this one.

[avr1254]

A question about unpacking: how do I unwrap a Document from DomRoot? I'm pretty sure it's not unwrap(), but I couldn't find a suitable function in root.rs. This unwrap would be useful for step 2 of getting an element's target.

[jdm]

DomRoot<T> automatically dereferences to &T when you use * or call a method on the underlying T type. You can see the documentation at https://doc.servo.org/script/dom/bindings/root/type.DomRoot.html.

[avr1254]

Great, thanks!

[avr1254]

Another question, how do I gain access to a specific button wrapped in the enum FormSubmitter? I'm trying to check whether or not the submit button has a formtarget attribute value.

[jdm]

@avr1254 It's an enum:

pub enum FormSubmitter<'a> {
    FormElement(&'a HTMLFormElement),
    InputElement(&'a HTMLInputElement),
    ButtonElement(&'a HTMLButtonElement),
}

You can match on it (or use if let FormSubmitter::InputElement(input) = input) and get access to the inner pointer to the DOM object.