message index

I'm using the following Java to interface with leafnode:

getMessages

public Message[] getMessages(int start,
                              int end)
             throws MessagingException

     Returns the messages in the given range (inclusive).

     Parameters:
         start - the number of the first message
         end - the number of the last message

http://www.gnu.org/software/classpathx/javamail/javadoc/javax/mail/
Folder.html#getMessages%28int,int%29

but just wanted to clarify how the nntp protocol and leafnode work a bit.

Is it correct that messages in a folder are numbered 1..n?  Is it, unless 
maybe in the middle of an operation, continuous, or can there be 
discontinuities?

I ask because I suppose it's possible to work at a lower level then GNU 
package, or retrieve messages individually, but it's much easier to a 
range of messages, as above, provided there are no missing messages or 
gaps.



thanks,

Thufir