How can the presence of multiple occurrences of a character affect the accuracy of substring extraction in PHP?

When there are multiple occurrences of a character in a string, it can affect the accuracy of substring extraction in PHP because functions like `substr()` will only extract the substring up to the first occurrence of the character. To accurately extract substrings, you can use functions like `strpos()` to find the position of the first occurrence of the character and then use `substr()` with that position as the starting point.

$string = "hello world, hello universe";
$char = "o";
$pos = strpos($string, $char);
$substring = substr($string, $pos);
echo $substring; // Output: o world, hello universe