I wrote and use an editor similar to Scrivener that allows the user to edit in Markdown, but saves the project as XML. Images are saved as nodes with a mimetype

I wrote and use an editor similar to Scrivener that allows the user to edit in Markdown, but saves the project as XML. Images are saved as nodes with a mimetype and a Base64-encoded byte array, and referenced in the document with a UUID. HTML also allows you to specify an image inline using Base64 encoding; soemthing like <img src="data:image/png;base64, fhfhfhfh..."> I don't know what FB2 does, but it's definitely a solvable problem.