Convert the string you are searching in to lowercase, then use strpos or strstr. You can merge the above two steps if you do not want two distinct passes of the string. The docs themselves recommend using strpos/strstr over using a regex as they will be faster.
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stripos does a case insensitive search. Its faster than any other method as it runs within the C code for PHP instead of using the regex parser which is slower.
One thing to always remember, if there is a built-in PHP function that can do a string manipulation for you, always use that before any regex option as it is always faster.
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