idlwave-shell-mark-stop-line

idlwave-shell-mark-stop-line is a variable defined in `idlw-shell.el'.
Its value is

t

Documentation:
Non-nil means, mark the source code line where IDL is currently stopped.
Value decides about the method which is used to mark the line. Valid values
are:

nil Do not mark the line
'arrow Use the overlay arrow
'face Use `idlwave-shell-stop-line-face' to highlight the line.
t Use what IDLWAVE thinks is best. Will be a face where possible,
otherwise the overlay arrow.
The overlay-arrow has the disadvantage to hide the first chars of a line.
Since many people do not have the main block of IDL programs indented,
a face highlighting may be better.
In Emacs 21, the overlay arrow is displayed in a special area and never
hides any code, so setting this to 'arrow on Emacs 21 sounds like a good idea.

You can customize this variable.