wp_sprintf( string $pattern, mixed $args )

function wp_sprintf( $pattern ) {
	$args = func_get_args();
	$len = strlen($pattern);
	$start = 0;
	$result = '';
	$arg_index = 0;
	while ( $len > $start ) {
		// Last character: append and break
		if ( strlen($pattern) - 1 == $start ) {
			$result .= substr($pattern, -1);
			break;
		}

		// Literal %: append and continue
		if ( substr($pattern, $start, 2) == '%%' ) {
			$start += 2;
			$result .= '%';
			continue;
		}

		// Get fragment before next %
		$end = strpos($pattern, '%', $start + 1);
		if ( false === $end )
			$end = $len;
		$fragment = substr($pattern, $start, $end - $start);

		// Fragment has a specifier
		if ( $pattern[$start] == '%' ) {
			// Find numbered arguments or take the next one in order
			if ( preg_match('/^%(\d+)\$/', $fragment, $matches) ) {
				$arg = isset($args[$matches[1]]) ? $args[$matches[1]] : '';
				$fragment = str_replace("%{$matches[1]}$", '%', $fragment);
			} else {
				++$arg_index;
				$arg = isset($args[$arg_index]) ? $args[$arg_index] : '';
			}

			/**
			 * Filters a fragment from the pattern passed to wp_sprintf().
			 *
			 * If the fragment is unchanged, then sprintf() will be run on the fragment.
			 *
			 * @since WP-2.5.0
			 *
			 * @param string $fragment A fragment from the pattern.
			 * @param string $arg      The argument.
			 */
			$_fragment = apply_filters( 'wp_sprintf', $fragment, $arg );
			if ( $_fragment != $fragment )
				$fragment = $_fragment;
			else
				$fragment = sprintf($fragment, strval($arg) );
		}

		// Append to result and move to next fragment
		$result .= $fragment;
		$start = $end;
	}
	return $result;
}