IBM 3270 User Manual page 43

Hold the Tab key down. The cursor stops not
only at tab stops, but also at other positions on the line.
These other positions are unprotected fields, and the
cursor stops at them just as it always did when you used
the Tab key.
Press the Back Tab key. The cursor stops at the
same positions as it moves in the reverse direction.
Use these keys to move the cursor around to get a feel for
how they operate.
The following is an example of some columns of numbers.
You can enter such columns by using the Tab key to rapidly position
the cursor to the beginning position of each column:
0808 0808
97979
0808
8080
98088
0808
0808
80800
8008
9797 77575
In the blank area below, enter some columns
of numbers of your own choosing. Use the Tab key
to position the cursor to the column positions.
Remember the following things about using the Tab key:
In some situations, the Tab key inserts space characters that
can change the way your printed document looks.
When document mode is off, the Tab key moves
the cursor to the next unprotected field. ^ ^
When document mode is on, the Tab key moves the cursor
to the next unprotected field or to the next tab stop,
whichever comes first.
If the cursor moves to a tab stop, it may also replace null characters
with space characters in the unprotected positions that
the cursor passes over. This preserves the spacing between the
columns of data when the data is sent to the host.
Clear all tab stops first to avoid entering space characters
during tabbing operations.
Now let's try some other things.
5-6 Entry Assist User's Guide