I want to understand the RGNDATAHEADER structure for DirectDrawClippe

I came across this code for DirectDraw cLipper in my book

LPRGNDATA region_data
=(LPRGNDATA)malloc(sizeof(RGNDATAHEADER)+num_rects *sizeof(RECT));
memcpy(region_data->Buffer, clip_list, sizeof(RECT)*num_rects);

region_data->rdh.dwSize =sizeof(RGNDATAHEADER);
region_data->rdh.iType =RDH_RECTANGLES;
region_data->rdh.nCount =num_rects;
region_data->rdh.nRgnSize =num_rects*sizeof(RECT);

region_data->rdh.rcBound.left =64000;
region_data->rdh.rcBound.top =64000;
region_data->rdh.rcBound.right =-64000;
region_data->rdh.rcBound.bottom =-64000;

int i;
for (i=0; i<num_rects; i++)
{

// On regarde si le rectangle courant dépasse de la région
if(clip_list[i].leftrdh.rcBound.left)
{

region_data->rdh.rcBound.left=clip_list[i].left;

}
if(clip_list[i].right>region_data->rdh.rcBound.right)
{

region_data->rdh.rcBound.right=clip_list[i].right;

}
if(clip_list[i].toprdh.rcBound.top)
{

region_data->rdh.rcBound.top=clip_list[i].top;

}
if(clip_list[i].bottom>region_data->rdh.rcBound.bottom)
{

region_data->rdh.rcBound.bottom=clip_list[i].bottom;

}

}



I'm trying to figure out why would someone would put 64000 and -64000 for
the region_data->rdh.rcBound RECT and why would we need to check for the
region in the code just after. This is is the only thing that I need to know
since the rest is pretty clear



thanks for your time !