This method, like mb_ereg_search_pos, appears to use byte offsets, not character offsets. This seems counter intuitive for the mb_* methods, which inherently take a "character" view of strings, as opposed to a "byte" based view. Even the mb_strpos method returns a character offset.The following code reveals this byte-oriented behaviour:<?php $x = 'abc456789'. "\u{1000}" .'abc4567890'; $re = 'ab.'; echo 'x='. $x .PHP_EOL; echo 're='. $re .PHP_EOL; mb_ereg_search_init( $x ); mb_internal_encoding( mb_detect_encoding( $x) ); echo 'mb_strlen='. mb_strlen( $x ) .PHP_EOL; echo 'strlen='. strlen( $x ) .PHP_EOL; foreach ( array( 0, 9, 10, 11, 12, 13 ) as $o ) { mb_ereg_search_setpos( $o ); echo 'Offset='. $o .' mb_substr='. mb_substr( $x, $o ) .' substr='. substr( $x, $o ) .' mb_ereg_search_regs='. print_r( mb_ereg_search_regs( $re ), true ) .PHP_EOL; }?>With character offsets, we would expect offsets 11 and above to return no search result, whereas what we see is:<?php=abc456789ကabc4567890re=ab.mb_strlen=20strlen=22Offset=0 mb_substr=abc456789ကabc4567890 substr=abc456789ကabc4567890 mb_ereg_search_regs=Array( [0] => abc)Offset=9 mb_substr=ကabc4567890 substr=ကabc4567890 mb_ereg_search_regs=Array( [0] => abc)Offset=10 mb_substr=abc4567890 substr=��abc4567890 mb_ereg_search_regs=Array( [0] => abc)Offset=11 mb_substr=bc4567890 substr=�abc4567890 mb_ereg_search_regs=Array( [0] => abc)Offset=12 mb_substr=c4567890 substr=abc4567890 mb_ereg_search_regs=Array( [0] => abc)Offset=13 mb_substr=4567890 substr=bc4567890 mb_ereg_search_regs=?>
