[TOC] ## string.rot13 字母后移13位 ``` $fp = fopen("php://output",'wb'); stream_filter_append($fp,"string.rot13"); fwrite($fp,"123abc"); // 123nop ``` ## string.toupper / string.tolower ``` $fp = fopen("php://output",'wb'); stream_filter_append($fp,"string.toupper"); fwrite($fp,"123abc"); // 123ABC ``` ## string.strip_tags ``` $fp = fopen('php://output', 'wb'); stream_filter_append($fp, 'string.strip_tags'); fwrite($fp, "<b>bolded text</b> enlarged to a <h1>level 1 heading</h1>\n"); fclose($fp); // bolded text enlarged to a level 1 heading ```