Contact emails
[email protected]

Specification
https://drafts.csswg.org/css-backgrounds-4/#background-position-longhands


Summary
Defines the background image's position relative to one of its edges. This 
syntax gives web authors a more flexible and responsive mechanisms to define 
the background image position, instead of using fixed values that need to be 
adapted to the window's or frame's size. This feature is applied also to the 
"-webkit-mask-position" to ensure webcompat levels are the same.


Blink component
Blink>CSS


Web Feature ID
background-position


Motivation
One important motivation is interoperability, given that Chrome is the only 
browser that lacks this syntax for the background-position-x/y longhands. 
Additionally, the background-position shorthand, which sets both the x/y 
positions, already supports the side-relative syntax, so the lack of the same 
syntax in the longhands may confuse web developers. There is no specific 
explainer, but this MDN page should be enough to understand the feature: 
https://developer.mozilla.org/en-US/docs/Web/CSS/background-position-x


Initial public proposal
No information provided


TAG review
No information provided


TAG review status
Not applicable


Risks




Interoperability and Compatibility
This feature doesn't imply any interoperability risk, but the contrary, since 
Chrome needs to catch up in order to provide the same functionality than 
Firefox and Safari. There is no back-compatibility risk, because the old syntax 
is still valid if this feature is implemented.

Gecko: Shipped/Shipping

WebKit: Shipped/Shipping

Web developers: Positive (https://issues.chromium.org/issues/40468636) The 
issue has 15 votes by now.

Other signals:


WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it 
has potentially high risk for Android WebView-based applications?
No information provided



Debuggability
The feature can be tested and debugged using the regular Chrome DevTools 
support (eg, css style inspection)


Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, 
ChromeOS, Android, and Android WebView)?
Yes
This feature is implemented in the blink's style module of the web engine, so 
it's shared among all the platforms.


Is this feature fully tested by web-platform-tests?
Yes
https://wpt.fyi/results/css/css-backgrounds/parsing?label=master&label=experimental&aligned&q=background-position-x
 
https://wpt.fyi/results/css/css-backgrounds/parsing?label=master&label=experimental&aligned&q=background-position-y


Flag name on about://flags
No information provided


Finch feature name
No information provided


Non-finch justification
This is a catch-up change to align Chrome with the rest of the major web 
engines (Firefox and Safari). It affects blink only and enables a new syntax 
for a CSS property that Chrome already exposes to the web.


Rollout plan
Will ship enabled for all users


Requires code in //chrome?
False


Tracking bug
https://issues.chromium.org/issues/40468636


Estimated milestones


Shipping on desktop 143

Shipping on Android 143

Shipping on WebView 143




Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop 
issues. Please list open issues (eg links to known github issues in the project 
for the feature specification) whose resolution may introduce web 
compat/interop risk (eg, changing to naming or structure of the API in a 
non-backward-compatible way).
No information provided


Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5073321259565056?gate=5131252113997824


Links to previous Intent discussions
Intent to Prototype: 
https://groups.google.com/a/chromium.org/d/msgid/blink-dev/68d10a08.710a0220.5367c.009d.GAE%40google.com



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