ImageTypeCommand: Provide Configuration For "Is Valid Image" (other than default relying on src/uploadId attribute)

[mmichaelis]

📝 Provide a description of the improvement

When it comes to using the ImageTypeCommand for images, for example, served from a CMS, the image model representation may miss a src attribute depending on the overall design.

Having this, image types ImageInline and ImageBlock cannot be toggled via ImageTypeCommand due to its hard-wired restriction to only work on images with valid src attribute (or as the only alternative, the uploadId).

See:

ckeditor5/packages/ckeditor5-image/src/image/imagetypecommand.ts

Lines 66 to 71 in b5c31df

	// Don't change image type if "src" is missing (a broken image), unless there's "uploadId" set.
	// This state may happen during image upload (before it finishes) and it should be possible to change type
	// of the image in the meantime.
	if ( !attributes.src && !attributes.uploadId ) {
	return null;
	}

Our scenario requires a different approach (similar to the uploadId), that may benefit from some redesign to copy with the ImageTypeCommand restrictions, but just to sketch our scenario:

• Our images are represented by an image element (custom grammar, no HTML; roughly sketched example):

  <img xlink:href="content/42"/>

• The xlink:href denotes the "strategy to retrieve the image BLOB data".

• In editing view, we load the BLOB lazily (and show a placeholder meanwhile) by eventually setting the src attribute to the "resolved BLOB data location". This src attribute later must not be stored in data layer (we currently prevent it even to appear in the model layer by blocking the corresponding upcast).

Thus, src is never part of the model, but instead some ID similar to uploadId.

💡 Suggestion

As possibly more concrete use-case, remove the hard-wired uploadId from ImageTypeCommand as it is a forward-reference to a possibly not even installed plugin.

Instead, let the image upload plugin use some to be specified API to register this "alternative src attribute", so that the ImageTypeCommand may respect it.

This API then could also be used by other image architectures like ours.

📃 Other details

• Browser: Chrome
• OS: Windows
• CKEditor version: 39.0.2
• Installed CKEditor plugins: Image

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[Witoso]

Thanks for the request, we will discuss it internally.

[CKEditorBot]

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