Selection range is incorrect when selecting across multiple elements

Phenomenon

When selecting text that spans across multiple HTML elements (e.g., <p>, <div>, <span>) in a contenteditable region, the selection range may not accurately reflect the visual selection. The Selection and Range APIs may return incorrect boundaries.

Reproduction example

1. Create a contenteditable div with nested elements:

   <div contenteditable>
     <p>First paragraph</p>
     <p>Second paragraph</p>
   </div>

2. Select text that spans from the middle of the first paragraph to the middle of the second paragraph.
3. Use JavaScript to inspect the selection range.
4. Observe the reported start and end positions.

Observed behavior

• In Edge on Windows, the selection range boundaries may not match the visual selection.
• The Range.startOffset and Range.endOffset may be incorrect.
• Selecting across element boundaries can produce unexpected results.

Expected behavior

• The selection range should accurately reflect the visual selection.
• Boundaries should be correctly reported even when spanning multiple elements.
• The Selection and Range APIs should provide consistent, reliable data.