<?php
/*
Plugin Name: Periods in Title
Version: 1.0
Description: Allows periods to appear in post/category URIs
Author: Mark Jaquith
Plugin URI: http://txfx.net/code/wordpress/periods-in-titles/
Author URI: http://txfx.net/
*/

remove_filter('sanitize_title', 'sanitize_title_with_dashes');

function sanitize_title_with_dots_and_dashes($title) {
	$title = strip_tags($title);
	// Preserve escaped octets.
	$title = preg_replace('|%([a-fA-F0-9][a-fA-F0-9])|', '---$1---', $title);
	// Remove percent signs that are not part of an octet.
	$title = str_replace('%', '', $title);
	// Restore octets.
	$title = preg_replace('|---([a-fA-F0-9][a-fA-F0-9])---|', '%$1', $title);

	$title = remove_accents($title);
	if (seems_utf8($title)) {
		if (function_exists('mb_strtolower')) {
			$title = mb_strtolower($title, 'UTF-8');
		}
		$title = utf8_uri_encode($title);
	}

	$title = strtolower($title);
	$title = preg_replace('/&.+?;/', '', $title); // kill entities
	$title = preg_replace('/[^%a-z0-9 ._-]/', '', $title);
	$title = preg_replace('/\s+/', '-', $title);
	$title = preg_replace('|-+|', '-', $title);
	$title = trim($title, '-');
	$title = str_replace('-.-', '.', $title);
	$title = str_replace('-.', '.', $title);
	$title = str_replace('.-', '.', $title);
	$title = preg_replace('|([^.])\.$|', '$1', $title);
	$title = trim($title, '-'); // yes, again

	return $title;
}

add_filter('sanitize_title', 'sanitize_title_with_dots_and_dashes');
?>