http://docs.moodle.org/dev/Coding_style#Require_.2F_include

Two problems:

1. This does not mention that you should use require_once except for config.php, which should use require.

2. I think there should be an example of correctly requiring another file.

Suggest rewrite of this paragraph:

Any other include/require should use an absolute path starting with $CFG->dirroot or $CFG->libdir or path starting with _FILE_ or _DIR_. Relative includes starting with "../" can sometimes behave strangely under PHP, so it is safer to avoid them. Our CLI script must not use relative config.php paths starting with "../".

To this:

Any other include/require should use a path starting with _DIR_ or an absolute path starting with $CFG->dirroot or $CFG->libdir. Relative includes starting with "../" can sometimes behave strangely under PHP, so should not be used. Our CLI scripts must not use relative config.php paths starting with "../".

For library files in normal usage, require_once should be used (this is different from config.php which should always use 'require' as above). Examples:

require_once(_DIR_ . '/locallib.php');
require_once($CFG->libdir . '/filelib.php');

NOTE: I don't know if there's something wrong with Jira or what but I had to use Firefox to make the select box for components unhidden in order to submit this issue, nice...