Draft.js doesn't use the native browser content editable behaviour. It ensures that only valid markup can be generated: all text exists in a single block level

Draft.js doesn't use the native browser content editable behaviour. It ensures that only valid markup can be generated: all text exists in a single block level element (p, h1, h2, li, blockquote) and then inline text can have an number of a developer-defined formatting options applied (emphasis, bold, links). It doesn't have the compatibility problems and ambiguity that markdown suffers from.