How can PHP developers handle input fields that may contain spaces, like in the case of city names, when using Regular Expressions for validation?

When using Regular Expressions for validation in PHP, developers can handle input fields that may contain spaces by including the "\s" metacharacter in their regex pattern. This metacharacter matches any whitespace character, including spaces. By including "\s" in the pattern, developers can ensure that input fields like city names with spaces are properly validated.

// Example code snippet
$cityName = "New York";

// Regular Expression pattern to validate city names with spaces
$pattern = "/^[a-zA-Z\s]+$/";

if (preg_match($pattern, $cityName)) {
    echo "City name is valid.";
} else {
    echo "Invalid city name.";
}