text and images are not allowed immediately inside the body element, and need to be contained in a block level element like p or div
input elements must not be direct descendants of a form element
text in blockquote elements must be wrapped in a block level element like p or div

所以，我认为，在strict型必须用块级元素将引用文字包含，而在非strict型中就不必了，但是建议这样这样做，因为strict型文档更严格，也算是向后兼容了。