is_exposed.i4.v = window_gap_c(window_id.i2.v, row.i4.v,
				       left_column.i4.v, num_columns.i4.v)

	This routine returns a value of FALSE if the requested field in
	the window indicated by "window_id" is occluded (either partially or
	completely) by another window.

	window_id	window ID (use WMNGR_BACKGROUND for background window)
	row		row of field in full screen coordinates
	left_column	left column of field in full screen coordinates
	num_columns	length of field in columns

	This function returns status values as follows:

	TRUE			field is exposed
	FALSE			field is occluded

	This function requires the following include files:

	cnsparam_h, cbslib_h

	Related functions:

	window_gap_length_c, window_exposed_region_c, window_hole_c,
	screen_row(_c), screen_column(_c), in_window_field(_c), intro_tv_windows

	C/C++ usage:

	short	window_id;
	int	is_exposed;
	int	row = 1;
	int	left_column = 1;
	int	num_columns = 10;

	row = screen_row_c(window_id,row);
	left_column = screen_column_c(window_id,left_column);

	is_exposed = window_gap_c(window_id,row,left_column,num_columns);