What best practices should be followed when replacing multiple instances of a pattern using regular expressions in PHP?

When replacing multiple instances of a pattern using regular expressions in PHP, it is important to use the `preg_replace()` function with the appropriate flags to ensure all instances are replaced. The `preg_replace()` function allows for the use of the `g` flag to replace all instances of the pattern, and the `i` flag for case-insensitive matching. Additionally, using capturing groups `( )` in the pattern can help preserve parts of the original string in the replacement.

// Example code snippet for replacing multiple instances of a pattern using regular expressions in PHP
$string = "The quick brown fox jumps over the lazy dog.";
$pattern = "/brown/i";
$replacement = "red";

// Replace all instances of the pattern with the replacement using preg_replace
$new_string = preg_replace($pattern, $replacement, $string);

echo $new_string; // Output: "The quick red fox jumps over the lazy dog."