/p>

This editor is using a custom configuration for ACF. Note that filters can be configured as an object literal as an alternative to a string-based definition.

CKEDITOR.replace( 'editor3', {
	allowedContent: {
		'b i ul ol big small': true,
		'h1 h2 h3 p blockquote li': {
			styles: 'text-align'
		},
		a: { attributes: '!href,target' },
		img: {
			attributes: '!src,alt',
			styles: 'width,height',
			classes: 'left,right'
		}
	}
} );

This editor is using a custom set of plugins and buttons.

CKEDITOR.replace( 'editor4', {
	removePlugins: 'bidi,font,forms,flash,horizontalrule,iframe,justify,table,tabletools,smiley',
	removeButtons: 'Anchor,Underline,Strike,Subscript,Superscript,Image',
	format_tags: 'p;h1;h2;h3;pre;address'
} );

As you can see, removing plugins and buttons implies filtering. Several tags are not allowed in the editor because there's no plugin/button that is responsible for creating and editing this kind of content (for example: the image is missing because of removeButtons: 'Image'). The conclusion is that ACF works "backwards" as well: modifying UI elements is changing allowed content rules.