did_it.i4.v = btvblnk(row.i4.r, column.i4.r, num_chars.i4.r

	did_it.i4.v = btvblnk_c(row.i4.v, column.i4.v, num_chars.i4.v

	This routine will write one or more blanks to the background text
	window.  This routine is a replacement for 'tvblnk(_c)' for
	applications utilizing window management.

	row, column	starting screen coordinate location
	num_chars	number of blanks to write
	[color]		color of blanks (default is BLACK)
			(constants are in 'cnsparam')

	This function returns status values as follows:

	TRUE			window I/O actually done
	FALSE			no window I/O done

	This function requires the following include files:

	cnsparam_h, cbslib_h

	Related functions:

	window_blank(_c), window_erase_line(_c), window_erase_to_eol_c,
	window_erase_c, intro_tv_windows

	C/C++ usage:

	int	did_it;
	int	row = 1;
	int	column = 1;
	int	num_chars = 0;
	int	color = BLACK;

	did_it = btvblnk_c(row,column,num_chars,color);