Every PHP script you create should immediately open with a full GPL copyright statement. This is followed by a separate docblock statement that needs to contain the following:

<?php 
// This file is part of Moodle - http://moodle.org/ 
// 
// Moodle is free software: you can redistribute it and/or modify 
// it under the terms of the GNU General Public License as published by 
// the Free Software Foundation, either version 3 of the License, or 
// (at your option) any later version. 
// 
// Moodle is distributed in the hope that it will be useful, 
// but WITHOUT ANY WARRANTY; without even the implied warranty of 
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
// GNU General Public License for more details. 
// 
// You should have received a copy of the GNU General Public License 
// along with Moodle.  If not, see...