What alternative functions in PHP can be used for case-insensitive word replacement in a string?

When replacing words in a string in PHP, the `str_ireplace()` function can be used for case-insensitive replacements. This function works similarly to `str_replace()`, but it ignores the case of the words being searched for. This can be useful when you want to replace a word regardless of its case in the input string.

$inputString = "The quick brown fox jumps over the lazy dog.";
$wordToReplace = "fox";
$replacementWord = "cat";

$outputString = str_ireplace($wordToReplace, $replacementWord, $inputString);

echo $outputString;