Z-Machine re: set_text_style

From ZSpec 1.0, section

On the surface this appears to say that in V6, text styles behave “just as” they do in V4. Is the parenthetical remark an elaboration of the V4 behavior or an extrapolation into V6 behavior?

In other words, in the V4 model, are text styles set for the current window, or for all windows?

Border Zone appears to expect the latter, and that is what Windows Frotz implements. Tor went the other way with Glk Frotz, presumably owing to the ambiguity of the spec.

In V4, there’s no concept of different styles for different windows: there’s just the current style, which applies wherever the output appears. V6 introduces 8 windows, each with their own style, and V6 @set_text_style then operates on the current window, which is I believe what the parenthetical remark is trying to say.

This is also how the core Frotz code implements it, not just Windows Frotz.