Span the first word ya dingus

first-word

$string = 'Test me more';
$pattern = '/^(\S+)/';
$replacement = '<span class="first-word">$1</span>';
echo preg_replace($pattern, $replacement, $string);

// or

echo preg_replace('/^(\S+)/', '<span class="first-word">$1</span>', 'Test me more');

// from @greg5green

/^(\S+)/ = at the start of the string, match between 1 and infinite number of characters that are not whitespace characters
^ = start of string
\S = not whitespace characters
+ = 1 to infinity