public function license_key() {
			$field = $this->do_field_start();
			$field .= $this->do_field_label();
			$field .= $this->do_field_div_start();
			$field .= '<input';
			$field .= ' type="text"';
			$field .= $this->do_field_name();
			$field .= $this->do_field_value();
			$field .= $this->do_field_attributes();
			$field .= '/>';
			$field .= '<p class="license-test-results"><img src="' . esc_url( admin_url( 'images/wpspin_light.gif' ) ) . '" class="ajax-loading-license" alt="Loading" style="display: none"/>';
			$field .= '<span class="key-validity"></span>';
			$field .= $this->do_screen_reader_label();
			$field .= $this->do_field_div_end();
			$field .= $this->do_field_end();

			return $field;
		}