Bug 248432

Instead it should probably be removed. 
https://bugs.chromium.org/p/chromium/issues/detail?id=940652

With 
```
data:text/html,<div%20style="line-height:2em;%20height:9em;%20overflow:-webkit-paged-y;%20background:yellow;">%20%20%20%20%20scroll%20me<br>%20%20%20%20%20Please%20scroll%20me<br>%20%20%20%20%20Pretty%20please%20scroll%20me<br>%20%20%20%20%20Pretty%20please%20scroll%20me!<br>%20%20%20%20%20This%20is%20where%20page%202%20starts<br>%20%20%20%20%20more%20page%202%20content<br>%20%20%20%20%20even%20more%20page%202%20content<br>%20%20%20%20%20PASS%20</div>
```

and `window.getComputedStyle(document.querySelector('div')).overflow`

Safari: `auto -webkit-paged-y`
Firefox: `visible`
Chrome: `visible`


https://searchfox.org/wubkat/search?q=WebkitPaged&path=&case=false&regexp=false

<rdar://problem/103000377>

(In reply to Karl Dubost from comment #1)
> Instead it should probably be removed. 
> https://bugs.chromium.org/p/chromium/issues/detail?id=940652
> 
> With 
> ```
> data:text/html,<div%20style="line-height:2em;%20height:9em;%20overflow:-
> webkit-paged-y;%20background:yellow;
> ">%20%20%20%20%20scroll%20me<br>%20%20%20%20%20Please%20scroll%20me<br>%20%20
> %20%20%20Pretty%20please%20scroll%20me<br>%20%20%20%20%20Pretty%20please%20sc
> roll%20me!
> <br>%20%20%20%20%20This%20is%20where%20page%202%20starts<br>%20%20%20%20%20mo
> re%20page%202%20content<br>%20%20%20%20%20even%20more%20page%202%20content<br
> >%20%20%20%20%20PASS%20</div>
> ```
> 
> and `window.getComputedStyle(document.querySelector('div')).overflow`
> 
> Safari: `auto -webkit-paged-y`
> Firefox: `visible`
> Chrome: `visible`
> 
> 
> https://searchfox.org/wubkat/
> search?q=WebkitPaged&path=&case=false&regexp=false

Sweet! If we can remove it then it is better since then we would more web-compatible.

Why do we think removing this is safe? We generally don't remove things unless we are confident it's A) not used and B) causing us harm somehow

(In reply to Myles C. Maxfield from comment #4)
> Why do we think removing this is safe? We generally don't remove things
> unless we are confident it's A) not used and B) causing us harm somehow

I don't know about A, but regarding B, this can cause behavior differences on websites between Safari and other browsers which is undesirable.

Blink - Intent To Remove - https://groups.google.com/a/chromium.org/g/blink-dev/c/_UhJEz04sqA

__________

https://chromestatus.com/metrics/feature/timeline/popularity/1867

^ Usage is about 0.005%

_______

Firefox -> Never supported this.

Blink / Chrome -> Removed it in 2019.

_______

So Safari is only browser with support for this.

The question becomes are there other WebKit-powered applications using this specific feature?

Local Page:

>> Source/WebCore/rendering/style/RenderStyleConstants.h

Line 273 & 274: enum class Overflow : uint8_t

Remove 'PagedX' and 'PagedY'

>> Source/WebCore/style/StyleAdjuster.cpp:

Remove following FIXME:

// FIXME: Once we implement pagination controls, overflow-x should default to hidden
// if overflow-y is set to -webkit-paged-x or -webkit-page-y. For now, we'll let it
// default to auto so we can at least scroll through the pages.

and following:

// Call setStylesForPaginationMode() if a pagination mode is set for any non-root elements. If these
    // styles are specified on a root element, then they will be incorporated in
    // Style::createForm_document.
    if ((style.overflowY() == Overflow::PagedX || style.overflowY() == Overflow::PagedY) && !(m_element && (m_element->hasTagName(htmlTag) || m_element->hasTagName(bodyTag))))
        style.setColumnStylesFromPaginationMode(WebCore::paginationModeForRenderStyle(style));

>> Source/WebCore/rendering/style/RenderStyleConstants.cpp:

In 'TextStream& operator<<(TextStream& ts, Overflow overflow)'

Remove case Overflow::PagedX: and case Overflow::PagedY:

>> Source/WebCore/rendering/RenderBlockFlow.cpp

In 'RenderBlockFlow::willCreateColumns', delete following:

// If overflow-y is set to paged-x or paged-y on the body or html element, we'll handle the paginating in the RenderView instead.
    if ((style().overflowY() == Overflow::PagedX || style().overflowY() == Overflow::PagedY) && !(isDocumentElementRenderer() || isBody()))
        return true;

>> Source/WebCore/page/LocalFrameView.h:

Delete 'Pagination::Mode paginationModeForRenderStyle'

>> Source/WebCore/page/LocalFrameView.cpp:

Delete 'Pagination::Mode paginationModeForRenderStyle'

and following comment:

'Don't set it at all. Values of Overflow::PagedX and Overflow::PagedY are handled by applyPaginationToViewPort().'


and in LocalFrameView::applyPaginationToViewport(), change it to this (* Not sure on this one *):

void LocalFrameView::applyPaginationToViewport()
{
    auto* document = m_frame->document();
    auto* documentElement = document ? document->documentElement() : nullptr;
    if (!documentElement || !documentElement->renderer()) {
        setPagination(Pagination());
        return;
    }
    Pagination pagination;
    setPagination(pagination);
}

>> Source/WebCore/css/parser/CSSPropertyParser.cpp:

In 'CSSPropertyParser::consumeOverflowShorthand': Delete following:

// FIXME: -webkit-paged-x or -webkit-paged-y only apply to overflow-y. If this value has been
        // set using the shorthand, then for now overflow-x will default to auto, but once we implement
        // pagination controls, it should default to hidden. If the overflow-y value is anything but
        // paged-x or paged-y, then overflow-x and overflow-y should have the same value.
        if (xValueID == CSSValueWebkitPagedX || xValueID == CSSValueWebkitPagedY)
            xValueID = CSSValueAuto;

>> Source/WebCore/css/CSSValueKeywords.in:

Delete following:

// overflow
-webkit-paged-x
-webkit-paged-y

>> Source/WebCore/css/CSSProperties.json:

Delete following:


},
                {
                    "value": "-webkit-paged-x",
                    "status": "non-standard"
                },
                {
                    "value": "-webkit-paged-y",
                    "status": "non-standard"

>> Source/WebCore/css/CSSPrimitiveValueMappings.h:

In 'constexpr CSSValueID toCSSValueID(Overflow e)': Delete following cases: 'case Overflow::PagedX:' and 'case Overflow::PagedY:'


In 'template<> constexpr Overflow fromCSSValueID(CSSValueID valueID)': Delete following cases: 'case CSSValueWebkitPagedX:' and 'case CSSValueWebkitPagedY:'

_____________

Just wanted to document for someone else to try locally.

@Karl - do you have any insight from internal Apple products perspective, which might rely on it?

I'm not sure, but it could probably be removed after the poking I have done internally. And given it has removed for a long time from chrome and was never be in Firefox. 

Content is probably not relying on it. 

Though on the other hand we can see things like

https://github.com/jarek-foksa/xel/blob/f977219f127492ab714e4b1c55c9726b6103aa29/themes/base.css#L792-L795


And comment like this
https://stackoverflow.com/questions/59599461/equivalent-to-uiwebviews-paginationmode-on-wkwebview


It is probably necessary to check if these cases have been solved. 


> Practically speaking these aren't used. Most developers use them accidentally, and typically when they are they force a new formatting context similar to setting overflow: hidden.
— https://developer.chrome.com/blog/chrome-75-deps-rems/