getContainingBlockElement method

Implementation

Element? getContainingBlockElement({CSSPositionType? positionType}) {
  Element? containingBlockElement;
  positionType ??= renderStyle.position;

  switch (positionType) {
    case CSSPositionType.relative:
    case CSSPositionType.static:
    case CSSPositionType.sticky:
      containingBlockElement = parentElement;
      break;
    case CSSPositionType.absolute:
      Element viewportElement = ownerDocument.documentElement!;

      // If the element has 'position: absolute', the containing block is established by the nearest ancestor with
      // a 'position' of 'absolute', 'relative' or 'fixed', in the following way:
      //  1. In the case that the ancestor is an inline element, the containing block is the bounding box around
      //    the padding boxes of the first and the last inline boxes generated for that element.
      //    In CSS 2.1, if the inline element is split across multiple lines, the containing block is undefined.
      //  2. Otherwise, the containing block is formed by the padding edge of the ancestor.
      containingBlockElement = _findContainingBlock(this, viewportElement);
      break;
    case CSSPositionType.fixed:
      Element viewportElement = ownerDocument.documentElement!;

      // For fixed positioning, the containing block is the viewport unless an
      // ancestor establishes a fixed-position containing block (e.g. transform).
      // https://drafts.csswg.org/css-position/#fixedpos-containing-block
      containingBlockElement =
          _findFixedContainingBlock(this, viewportElement) ?? viewportElement;

      break;
  }
  return containingBlockElement;
}