I/5802: Handle clipboard properly in restricte editing mode.

[jodator]

Suggested merge commit message (convention)

Feature: Allow pasting content into exception areas in restricted editing mode. Closes ckeditor/ckeditor5#5802.

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Additional information

• I've added a configuration for the text attributes that are allowed inside clipboard holder.

[jodator]

@Mgsy - it's an optimistic approach but should work. Could you check this PR with pasting in Restricted Editing mode?

• Only configured attributes should be allowed to be pasted (bold, italic, link by default).
• Paste (cut - also) should only occur when selection is fully inside exception.
• Copy should not be blocked.
• Pasting anything other than the text should be stripped down to basic text nodes (or stripped down entirely) - so only text content from tables, no images etc

[Mgsy]

@FilipTokarski, please check Chrome and Safari, I'll take Firefox.

[Mgsy]

Steps to reproduce

1. Go to http://localhost:8125/ckeditor5-restricted-editing/tests/manual/restrictedediting.html
2. Enter the restricted editing mode
3. Copy some link
4. Paste it to the exception marker

Current result

The plain text is pasted.

Expected result

The link is pasted.

[FilipTokarski]

The same in Chrome and Safari. Apart from this, seems to work fine.

[Reinmar]

Do we need the configuration for allowed attributes? Can't we have all text attributes allowed? Then, if I'm correct, it will be enough to add a callback allowing only $text in the $clipboardHolder. You won't need the other callback for attribute names. Schema works on the model so we can be very specific here allowing <$clipboardHolder>$text with all its attributes</$clipboardHolder> and nothing else. No reason for stuff like Array.from( context.getNames() ).includes( '$clipboardHolder' ) – it's enough to check the first item or add the ctx.startsWith() method.

[Reinmar]

As commented.

[jodator]

Do we need the configuration for allowed attributes?

In another way, we will get minor WTF if bold is allowed by command and you can bold text inside the non-restricted area but you can't paste it.

But we can also add this configuration later if requested so I can remove this from the PR.

[jodator]

@Reinmar: I've added the SchemaContext.startsWith() and fixed link attribute name used in default config.

[Reinmar]

Lookin' good 🍬!