What is the issue with the HTML Standard?

The only hint the specification gives at the moment is that it's called a "select popover". There's no normative requirements related to this.

Originally spotted here: #11729 (comment).

This also reminds me that I ran into some default style sheet conflicts between [popover] and ::picker(select) as we used the popover attribute to implement it. We needed various workarounds, such as:

[popover]:not(:popover-open):not(dialog[open]):not(:-internal-select-popover) {
    display: none;
}

[popover]:not(:-internal-select-popover) {
    inset: 0;
    margin: auto;
    border: solid;
    padding: 0.25em;
    color: CanvasText;
    background-color: Canvas;
}

(:-internal-select-popover being equivalent to ::picker(select).) I think these are real conflicts as the specificity of [popover] is too high. Of course, depending on how we specify this we might not run into this as we could delegate to some internal mechanism instead without using the attribute.

cc @emilio @keithamus @lukewarlow @nt1m