amp-invalid.php

<?php
/**
 * Plugin Name: AMP Invalid
 * Description: Do stuff that is invalid in AMP.
 */

namespace AMP_Invalid;

add_action( 'bad_amp_footer', function() {
	?>
	<div class="1">
		<script type="text/javascript">console.info('evil!');</script>
	</div>
	<?php
} );

// @todo This needs to be checked.
add_action( 'wp_enqueue_scripts', function() {
	wp_enqueue_style( 'plugin-css', plugin_dir_url( __FILE__ ) . 'plugin.css' );
	wp_enqueue_script( 'plugin-js', plugin_dir_url( __FILE__ ) . 'plugin.js', array(  ) );
	wp_enqueue_style( 'mu-plugin-css', plugins_url( '', WPMU_PLUGIN_DIR . '/' ) . 'mooo/mu-plugin.css' );
	wp_enqueue_script( 'mu-plugin-js', plugins_url( '', WPMU_PLUGIN_DIR . '/' ) . 'mooo/mu-plugin.js' );
	wp_enqueue_style( 'theme-css', get_template_directory_uri() . '/theme.css' );
	wp_enqueue_script( 'theme-js', get_template_directory_uri() . '/theme.js' );

	wp_enqueue_script( 'jquery' );
} );

add_shortcode( 'bad_amp', function() {
	return '<blockquote>Check out this <script>document.write("bad script");</script></blockquote>';
} );

add_action( 'wp_head', function() {
	?>
	<link rel="stylesheet" href="http://example.org/bad.css">
	<style>
		body { color: blue !important; }
	</style>
	<?php
} );

function footer_stuff() {
	?>
	<!-- before amp-keyframes -->
	<style amp-keyframes>
	@keyframes anim1 {}

	@media (min-width: 600px) {
		@keyframes anim1 {}
	}
	</style>
	<?php
	do_action( 'bad_amp_footer' );
}


add_action( 'wp_footer', __NAMESPACE__ . '\footer_stuff' );


add_action( 'widgets_init', function() {
	register_widget( __NAMESPACE__ . '\AMP_Invalid_Widget' );
} );

/**
 * Adds AMP_Invalid_Widget widget.
 */
class AMP_Invalid_Widget extends \WP_Widget {

	/**
	 * Register widget with WordPress.
	 */
	function __construct() {
		parent::__construct(
			'amp_invalid', // Base ID
			esc_html__( 'AMP Invalid', 'amp-invalid' ), // Name
			array( 'description' => esc_html__( 'A Foo Widget', 'amp-invalid' ), ) // Args
		);
	}

	/**
	 * Front-end display of widget.
	 *
	 * @see WP_Widget::widget()
	 *
	 * @param array $args     Widget arguments.
	 * @param array $instance Saved values from database.
	 */
	public function widget( $args, $instance ) {
		echo $args['before_widget'];
		if ( ! empty( $instance['title'] ) ) {
			echo $args['before_title'] . apply_filters( 'widget_title', $instance['title'] ) . $args['after_title'];
		}
		echo esc_html__( 'Hello, World!', 'amp-invalid' );
		echo "<script>document.write('hello')</script>";
		echo "<button onmouseenter=evil>clock me</button>";
		echo $args['after_widget'];
	}

	/**
	 * Back-end widget form.
	 *
	 * @see WP_Widget::form()
	 *
	 * @param array $instance Previously saved values from database.
	 */
	public function form( $instance ) {
		$title = ! empty( $instance['title'] ) ? $instance['title'] : esc_html__( 'New title', 'amp-invalid' );
		?>
		<p>
		<label for="<?php echo esc_attr( $this->get_field_id( 'title' ) ); ?>"><?php esc_attr_e( 'Title:', 'amp-invalid' ); ?></label>
		<input class="widefat" id="<?php echo esc_attr( $this->get_field_id( 'title' ) ); ?>" name="<?php echo esc_attr( $this->get_field_name( 'title' ) ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>">
		</p>
		<?php
	}

	/**
	 * Sanitize widget form values as they are saved.
	 *
	 * @see WP_Widget::update()
	 *
	 * @param array $new_instance Values just sent to be saved.
	 * @param array $old_instance Previously saved values from database.
	 *
	 * @return array Updated safe values to be saved.
	 */
	public function update( $new_instance, $old_instance ) {
		$instance = array();
		$instance['title'] = ( ! empty( $new_instance['title'] ) ) ? strip_tags( $new_instance['title'] ) : '';

		return $instance;
	}

} // class AMP_Invalid_Widget

plugin.css

body {
	color: green !important;
}