Editor can't do stylesheets...can it?

Really quick - can I mark up some bit of text as a header, and then later change the style of all headers? I don’t think that’s possible with the integrated editor, but I want to make sure.

DT doesn’t “do” headers or footers in the text editor.

If you need those, you might create a template of, for example, a Pages document with placeholder text in the header.