Source

File: wp-includes/Requests/Cookie.php

public function format_for_set_cookie() {
		$header_value = $this->format_for_header();
		if (!empty($this->attributes)) {
			$parts = array();
			foreach ($this->attributes as $key => $value) {
				// Ignore non-associative attributes
				if (is_numeric($key)) {
					$parts[] = $value;
				}
				else {
					$parts[] = sprintf('%s=%s', $key, $value);
				}
			}

			$header_value .= '; ' . implode('; ', $parts);
		}
		return $header_value;
	}