XML document sent by HTTP -> pl/sql stored procedure

Guys I need a 'kick-start' here - a 3rd party app wants to send us XML via a HTTP - how do I define my PL/SQL procedure to accept the input?

I had assumed the XML document would be sent almost as a single item of data which would correspond to an arg name in my PL/SQL procedure e.g.

create or replace procedure xml1

        (txtxml in clob default null)
is
..
..

And that the sending party would put the doc in a 'variable' named (in this case) txtxml.

There is something fundamental that I need to know but I don't know where to look! How is an XML document presented to my PL/SQL procedure?

The URL to which the data is to be sent will be say

http://myserver/plsql/xml1

Environemnt:
Oracle 9iR2 and Oracle HTTP Server (Apache 1.3.22) on Solaris 8.

Help please!

-- 

jeremy