n and m are optional (m cannot be specified without n).
n represents the width of the list-box in characters and m the
depth. n and m can be replaced by asterisks (*) in which case the
values of n and m must be supplied as the first two arguments in
the argument list.
num_items is the number of items in the list.
cur_item is the item number that is selected in the range zero to num_items
both on input and output. Zero signifies that no item is selected.
items is an array of text entries, one for each item. Blank entries at
the end of the list are not displayed. This means that you can use blank
entries to create a list that can be changed dynamically.
If the grave accent is used and a call-back is supplied, option can be
set to the keyword extended. The result is that the call-back is called when
the list drops down or closes up. These events must be detected from the
call-back by calling clearwin_string@('CALLBACK_REASON') which returns
'DROPDOWN' or 'CLOSEUP'.
For a list box (i.e. when a grave accent modifier is not used), the option
[hscrollbar] provides a horizontal scroll bar whilst the option [multicolumn]
provides a multiple column output (see
List box format).
If a grave accent is used (%`ls) and the parent window uses %sy - Dialog Style[3d_thin] then
%ls can be given the option [no_border] to reduce the thickness of the border.
The option [limit_height] takes an additional double precision argument (before
any callback function). This argument takes a value that should be less than
one. The maximum height of the control will be limited to this proportion
of the screen height.
If the grave accent modifier is not used, %ls can be preceded by a pivot %pv - Pivot.
grey_ctrl is 1 (enabled) or 0 (disable/greyed). Any call-back function
must be placed after this control variable.