Write a PHP function isPalindrome that accepts a string as a parameter and returns true if the string is a palindrome and false otherwise. A string is considered a palindrome if it has the same sequence of letters when reversed (for example, "radar","toot", "mom", "a", """"). Your function should be case-insensitive, for example, "Mom" and "RAdar" should be considered palindromes. Please also submit the html code you use to test the correctness of your function.