IBM 3270 User Manual page 43

Next, let's try some things that work only when your display is in
insert mode:
First, the backspace delete while in insert mode capability. This
capability undoes what a character insertion does. To try it, use the
Insert key (which you are already familiar with) to insert the word
last into the following sample sentence just in front of the word
time. After you have typed the word last, press the Backspace
Delete key to undo the insertion. Each pressing of the key deletes
the previous character and then backs the cursor up one position.
(The Backspace Delete key has the leftward-pointing arrow-the
top row of the keyboard just above the backtab key.) Remember,
this function operates only while insert mode is set.
Sample Sentence: This is the time.
We also need to understand how word wrap works when insert
mode is set. Turn on insert mode and make sure that word wrap is
on. Then insert enough words into the first sample sentence below
to force a word into the right margin and note how word wrap
works in insert mode. The words will wrap out of the first line into
the second line as long as there are sufficient trailing spaces or nulls
on the second line to accommodate them. When the next line
cannot accommodate the word, the keyboard
will
lock.
Sample Sentence: This is a sentence. This is a sample sentence.
Now let's try the cursor position indicator capability. Press the
CURS POS key. The current position of the cursor is displayed in
the bottom row of the display in the form rrlcc, where rr gives the
number of the row and cc gives the number of the column. Try it.
The rr/cc value remains displayed as long as you hold the ALT shift
key depressed.
Finally, you should be aware that line formats (margins, tab settings,
and an 'end of line' signal setting) are remembered as long as power
remains up at the 3274 Control Unit. You can verify this by turning
document mode off and then back on again. There will be no
change to your line formats. This is useful because, at times, it may
be necessary to exit document mode momentarily.
Section 5. Entry Assist Tutorial 37