CSS will-not-change

Question

There is a new CSS attribute, called will-change, using you can define properties which will be changed frequently, so the browser can optimize it. For example:

.element {
    will-change: transform, opacity;
}

But what about the opposite? Are there any suggestions or working drafts for something like will-not-change? Using it would be possible to hint the browser, that that properties will never change (constants), so it can do some optimizations on it?

Answer 1

Browsers already optimize their layout algorithms for properties that "will not change" by default. will-change is a way to opt properties in that might change (despite what the "will" in the property name might suggest) so browsers can perform the necessary optimizations beforehand for when those properties do change (from their initial value, at least).

Think of it this way: properties that aren't listed in will-change have already been optimized as "will not change", or "whether they change or not makes no meaningful difference in performance."

For example, your will-change declaration tells the browser to create a composition layer for .element elements, in the event that they need to be transformed or alpha composited, so that their rendering is hardware accelerated from the get-go. Since this will-change declaration doesn't apply to elements without this class, the browser assumes those other elements will never be transformed or alpha composited, and as such don't need this composition layer. By not creating composition layers for them, the browser has already optimized the rendering of those elements by not hardware accelerating them unnecessarily.