Bug 276926 – In a shadow root hosting element that has contenteditable=plaintext-only, the last inserted text node gets deleted as a whole instead of character-by-character

• Status: NEW
• Component: HTML Editing

[Zacky Ma]

Given an element like so:

```
<div contentediable=plaintext-only><template shadowrootmode="open"><slot></slot></template></div>
```

If a user type the following text character by character (as opposed to pasting the whole text with line breaks):

abc<Enter>
de<Enter>
fgh

Hit Backspace, "fgh" is deleted, caret moves right after "e", after this, hitting Backspace deletes character-by-character which is expected.

Seems if the container is a `<pre>` element, this issue doesn't occur.

Example: https://codepen.io/marchbox/pen/oNrLWjY

There is a previous unclosed bug here: https://bugs.webkit.org/show_bug.cgi?id=266700. But from my testing, seems `contenteditable=true` works fine, but `contenteditable=plaintext-only` doesn't.

[Zacky Ma]

Also, if you have the "Add period with double-space" feature turned on in macOS, double pressing Space also deletes the last added text node (and places the period right after any text that's left).

[Zacky Ma]

I tested a bit more:

- `contenteditable=true` does indeed still trigger this bug
- in addition to Backspacing the last line, when the caret is in the middle or beginning of a previous line, hitting Backspace also trigger this bug

[Radar WebKit Bug Importer]

<rdar://problem/132778602>