Xapian discuss - Feb 2009 - updated.size()

I took come code from http://trac.xapian.org/ticket/285.  It seems to 
work but I don;t understand what size has to do with it.

line 17408: 
if (docid < updated.size()) {
            updated[docid] = true;
            return;

On Wed, Feb 18, 2009 at 04:22:14AM +1030, Frank J Bruzzaniti
wrote:
> I took come code from http://trac.xapian.org/ticket/285.  It seems to 
> work but I don;t understand what size has to do with it.
> 
> line 17408: 
> if (docid < updated.size()) {
>             updated[docid] = true;
>             return;
Before indexing starts, updated is resized to include the highest
existing document id so if docid >= updated.size() it's a new document
not an updated one.

Cheers,
    Olly