Source

File: wp-includes/class-wp-customize-control.php

protected function render() {
		$id    = 'customize-control-' . str_replace( array( '[', ']' ), array( '-', '' ), $this->id );
		$class = 'customize-control customize-control-' . $this->type;

		printf( '<li id="%s" class="%s">', esc_attr( $id ), esc_attr( $class ) );
		$this->render_content();
		echo '</li>';
	}