カテゴリ／タクソノミをGETで受け取った時のバリデーション。Validate GET values against cattegories / taxonomies the site has.

gistfile1.php

<?php 
// example.com?what=abc&where=xyz

// category
$what = $_GET['what'];
$okCats = get_categories();
foreach ( $okCats as $oks ) {
	$okCatsArr[] = $oks->name;
}
$ifWhat = in_array($what, $okCatsArr);
$what = $ifWhat ? $what: $ifWhat;

// taxonomy (district)
$where = $_GET['where'];
$okDistrict = get_terms( 'district' );
foreach ( $okDistrict as $oks ) {
	$okDistrictArr[] = $oks->name;
}
$ifWhere = in_array($where, $okDistrictArr);
$where = $ifWhere ? $where: $ifWhere;

https://gist.github.com/4139916
こっちのほうが100倍よい。