IBM 3270 User Manual page 41

The following is an example of some columns of numbers that were
entered using the Tab key to rapidly position the cursor to the
column positions:
0808
0808
0808
8008
0808
8080
0808
9797
97979
98088
80800
77575
Use the following blank area to enter some columns of numbers of
your own choosing, using the Tab key to position the cursor to the
column positions.
You should be aware of one important point about using the Tab
key. When document mode is off, the Tab key merely 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. Also, if the move is to a tab
stop, it also replaces null characters with space characters in the
unprotected positions that the cursor passes over. This is necessary
to preserve the spacing between the columns of data when the data
is sent to the host. However, this introduction of space characters
could be a problem for a program not expecting it. In that case, you
can avert entry of space characters on tabbing operations by first
clearing all tab stops.
Section 5. Entry Assist Tutorial 35