<?php

$valid = [
	'%u003c%u0073%u0063%u0072%u0069%u0070%u0074%u003e',
	'%u003c',
	'%u0046%u005c',
];

$invalid = [
	'asd',
	'%a003da',
	'%k41ad',
	'Бла бла бла',
	'%u003c%u0073%u0063%',
	'%u003c%u0073ASFQ%u0063',
];


print("--- valid\n");
foreach ($valid as $value) {
	print("`$value` ".((preg_match ('/^(?:%u00[\da-z]{2})+$/' , $value, $matches)) ? 'valid' : 'invalid')."\n");
}
print("--- invalid\n");
foreach ($invalid as $value) {
	print("`$value` ".((preg_match ('/^(?:%u00[\da-z]{2})+$/' , $value, $matches)) ? 'valid' : 'invalid')."\n");
}