Allow specific tags to be added in the Wordpress content editor

gistfile1.txt

function mysite_allow_form_tags( $tags, $context) {

		$tags['form'] = array(
			'action' => true,
			'method' => true,
			'enctype' => true,
			'name' => true,
			'id' => true,
			'class' => true,
			'target' => true
		);

		$tags['input'] = array(
			'type' => true,
			'name' => true,
			'value' => true,
			'placeholder' => true,
			'required' => true,
			'autocomplete' => true,
			'autofocus' => true,
			'min' => true,
			'max' => true,
			'step' => true,
			'pattern' => true,
			'title' => true,
			'class' => true,
			'id' => true,
			'style' => true,
			// Allow JavaScript events
			'onblur' => true,
			'onchange' => true,
			'onclick' => true,
			'ondblclick' => true,
			'onfocus' => true,
			'onkeydown' => true,
			'onkeypress' => true,
			'onkeyup' => true,
			'onmousedown' => true,
			'onmousemove' => true,
			'onmouseout' => true,
			'onmouseover' => true,
			'onmouseup' => true,
			'onreset' => true,
			'onselect' => true,
			'onsubmit' => true,
			'oninvalid' => true,
		);

    return $tags;
}

add_filter( 'wp_kses_allowed_html', 'mysite_allow_form_tags', 10, 2 );