Isn't that the definition of separated? If you want to edit content or markup, you open the HTML file. If you want to edit business logic, open PHP or JS. And so on.
Yeah but then your JavaScript spews out unholy tendrils that mutate the DOM and dynamically add/remove CSS classes and style attributes. Separating HTML/CSS/JS made a lot of sense for web sites but separating by component makes more sense for web applications.
