(warning: now veering off even the metatopic)
Not as we define plaintext. The 3270s I remember were "all points
addressable". That is, there were code sequences in the data
stream that allowed "forms and fields" on the screen. Generally,
the operator only had access to the allowed fields.
For points=character-cells, yes. Okay, as you got below, I was talking
here about display enhancements (font variants/sizes, colors,
graphics) and not the datastream, and failed to distinguish.
327X *can* actually be used with a nearly-plain datastream, namely no
"orders" and only the initial command prefix (which is always
required); but this gives an unformatted display with the cursor in
home position, which is usually slow(er), easy(er) to produce garbled
input, and hard or impossible to give good feedback, so it wasn't
popular. I have actually used, and bitched at, some quick&dirty
utilities that did this. (You're right that) most 327X applications
use(d) forms containing protected/output and unprotected/input fields,
and TAB BACKTAB RETURN HOME go only to a protected field; (on a real
327X) if one uses the arrow keys to move to a protected area, or type
off the end of one field onto a non-skip protected field, and try to
type there, it "checks", and I think some emulators may not even allow
the movement.
A formatted field on 327X can also be invisible, and a common method
for "stateless" programming is to write to the screen buffer an
invisible protected field containing state data and flagged modified,
so on the next input operation (ENTER or PFnn) it is included along
with actual input data, and tells the program where to resume
processing; this is rather like HTTP (or HTML http-equiv) cookie or
HTML FORM HIDDEN field, except those don't take screen space.
And the VT escape codes that allowed a variety of things. Even
the VT100 series was "apa" -- escape sequences allowed you to put
the cursor anywhere you wanted.
I'm not sure about VT50; VT52 was directly addressable, but had IIRC
no display enhancements at all. VT10x had some enhancements, as I
mentioned, but not nearly all the ones you indicated earlier you would
want from HTML news. VT2xx added some and I believe 3xx more, but I
don't remember details there. All DEC terminals, and most other makers
as well, worked perfectly fine as a "glass TTY" with no commands at
all beyond the ASCII control characters (CR LF, maybe BS HT BEL) and
were commonly, I would estimate mostly, used that way. There were
specific applications that operated in "full screen" mode, especially
and most desirably editors, but any fields were created and protected
by the host receiving and screening each keystroke, although IIRC 2xx
added some minimal local checking capability.
You're right that What Was On The Screen was plaintext and typically
uppercase. The data stream that *put* it there was not.
Very much like HTML, actually....
Well, not that much. HTML was intended to be *structural* markup, and
although it has largely been (mis?)used for presentation w3c is trying
to drag it back toward structure. The orders and escape/command
sequences used on 327X and VTnnn, and indeed nearly all video
terminals, are almost entirely presentation, or communications
control. For example, one can't say "indent the following text block"
as you asked for at one point, much less "this is a block quote" or
"this is a stanza of poetry"; instead one must send each line (with a
correct break) with spaces and/or tabs prefixed. Although they do both
qualify as markup -- along with a huge number of other things,
including Usenet/textmail's > ** __
etc.
- David.Thompson1 at worldnet.att.net
