A diagram: 
beside text.
Images
An image is an inline atom: its source is a validated media reference, its alternative text belongs to the document.
Concept
Media boundary
ImageExtension stores references to finished media. Uploads and pickers belong to the application; undo removes the image node, not the uploaded file.
Inspect an image
The Markdown image becomes one atom in the tree. Empty alt text explicitly marks decorative images.
4 words · 5 nodes
ember.core.root/1 [document]
ember.rich-text.paragraph/1 [images5]
ember.core.text/1 [images1] "A diagram: "
ember.image.image/1 [images3]
ember.core.text/1 [images4] " beside text."
Source
Image commands
The application resolves a MediaReference through its media policy before dispatching InsertImage. UpdateImage keeps the node ID.
scala
val source = MediaUrlPolicy.default.unsafe("https://anjunar.com/diagram.png")
val image = ImageNode(
id = generator.nextFor(session.document),
source = MediaReference(source),
alt = "Architecture sketch"
)
session.dispatch(ImageCommands.InsertImage, image)
session.dispatch(ImageCommands.UpdateImage, _.copy(alt = "Updated diagram"))