Text, title and legend format

It’s not clear: are you trying to style the text for a plot title (which is always “outside” the central plot frame) or for some kind of label or text glyph (which is always “inside” the central plot frame)?

Regardless:

  • multi-line titles are not currently supported (but you can add multiple Title annotations that stack)
  • No “markup” is supported for styling in either case. For text or Label (or LabelSet) you could style individual words separately.