Help System (web edition)

The control column is the leftmost column (0) in the edit field.
It is usually filled with asterisks (*).
The normal way to reach the control column is to move the cursor to the
first column (by RETURN or arrow keys) and then press the left arrow
continuously.
The control column has following tasks:

Line labels consisting of one character (A,B,X,a,b,x) are typed in the
control column. Line labels can be used as line numbers in operations
referring to lines (PRINT X,Y). Since line labels are connected to the
lines (and do not alter when lines are inserted, deleted or moved) they
should in many applications be preferred to line numbers.
List of control characters in use in the current edit field is obtained by F1 L

In the PRINT operation characters ()/ in the control column determine
paging of the printout (see PRINT).

`?' in the control column hides the text and commands written on the
line in question (a useful feature in tutors and teaching programs).
`!' in the control column prohibits writing of text on the current line.
The line is then protected from inadvertent typing but can be deleted.
`_' in the control column prohibits writing and deleting of text on the
line in question.
'   in the control column has a special task in editorial computing.
Values of expressions on such a line will be displayed in `accurate'
exponential form (1.123456789012345e+123).

  C = Control operations 
  F = More information on the edit field