Do you need to turn whole web page into grayscale? We can do that only with CSS. Turn into grayscale mean all whole things on your web page: text, link color, image, border, background, even all external images on your web.
Need to remove everything after certain character inside PHP string? For example you willing to displaying only content after first / character, so we need PHP function to remove content before certain character.
We could remove everything after a certain character inside string in PHP. For example you willing to displaying only content before first < character, so we need PHP remove content after a certain character.