[cssom-view] offsetTop/Left spec seems to be pretty confused when scrolling is involved · w3c/csswg-drafts#1832

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描述

Simple testcase:

<div id="parent" style="overflow:scroll; height: 100px; position: relative">
  <div id="spacer" style="height: 200px"></div>
  <div id="child" style="border: 1px solid green"></div>
</div>

Load this, scroll the scrollable div all the way down, examine "child.offsetTop". It comes back as "200" in browsers. The spec at https://drafts.csswg.org/cssom-view/#dom-htmlelement-offsettop, on the other hand says:

Return the result of subtracting the y-coordinate of the top padding edge of the first CSS layout box associated with the offsetParent of the element from the y-coordinate of the top border edge of the first CSS layout box associated with the element, relative to the initial containing block origin, ignoring any transforms that apply to the element and its ancestors.

and in this case this is definitely not 200. The spec is wrong and needs to be fixed, afaict.

貢獻者指南

技術棧: csshtml
領域: frontend
議題類型: bug
難度: 3
預計時間: 1-3 hours
活動狀態: stale
清晰度: clear
前置要求: Understanding of CSS box modelFamiliarity with CSSOM offset properties
新手友善度: 40
研究方向: Review the current spec text at https://drafts.csswg.org/cssom view/#dom htmlelement offsettop and understand the scrolling behavior. Examine browser implementations (e.g., Chromium, Gecko) to see what value they return. The issue body provides a test case demonstrating the discrepancy. Propose a correction to the spec text that aligns with browser behavior. The issue may require discussion with the CSSWG.