[css-will-change] new property will-change-to

[Zhang-Junzhi]

I would like to suggest a new property will-change-to.

This is useful for some cases, for example, for preloading various external resources in an elegant pure CSS way:

html
{
    background-image: url(a);
    will-change-to: background-image, url(a), url(b), url(c);
}

html.theme-b
{
    background-image: url(b);
}

html.theme-c
{
    background-image: url(c);
}

This is just a simple example, and I have no idea of a specific format for multiple property support.

This new suggested will-change-to property can be seen as a version of will-change with specific property values added. There is also a difference between them: will-change signifies that the listed properties are constantly changing, while 'will-change-to' doesn't.