Pasting rich text into contenteditable strips markup unexpectedly

Phenomenon

When pasting content from a rich text source (such as a word processor or a web page) into a contenteditable element, the resulting DOM loses headings, lists, or inline formatting that were present in the source.

Reproduction example

1. Copy a short formatted snippet from another application or web page:
   • A heading
   • A bulleted or numbered list
   • A line with bold or italic text
2. Focus the editable area.
3. Paste the content using the keyboard shortcut or context menu.

Observed behavior

• The pasted content appears as plain text.
• List markers become plain characters, or multiple lines collapse into one.
• Inline styles such as bold or italic are not preserved in the DOM.

Expected behavior

• At least some structural markup (headings, lists, paragraphs) is preserved.
• Inline formatting is preserved or deliberately normalized in a documented way.

Notes

• Compare behavior across browsers and OS combinations using the same source content.
• Decide whether the product should preserve external markup, normalize it to a limited internal model, or always strip it to plain text.