html5与VS,HTML5中的vs

我一直难以决定何时使用b以及何时使用span.

b元素的新语义看起来很模糊.

The b element represents a span of text to which attention is being

drawn for utilitarian purposes without conveying any extra importance

and with no implication of an alternate voice or mood

听起来就像你不能使用strong,em或i时使用的标签.

The b element should be used as a last resort when no other element is

more appropriate.

但是,当短语内容还没有适用的标签时,我们已经获得了span.

The span element doesn’t mean anything on its own… It represents its

children.

有一个示例用途列表

key words in a document abstract,product names in a review,

actionable words in interactive text-driven software,or an article

lede

但是我找不到将它们联系在一起的基本原则,而不是将它们塑造成大胆的. old spec甚至提到了风格：

The b element represents a span of text to be stylistically offset

from the normal prose [emphasis added]

样式是为CSS.我们还建议使用类来显示实际含义

authors can use the class attribute on the b element to identify why

the element is being used

这听起来好像使用太多,不能单独按标签分组.我也可以使用类来解释span的语义.

The span element… can be useful when used together with the global

attributes,e.g. class,lang,or dir.

例子

如果我想要这个：

Your score for CS 101 Final is 42%.

我写吗

Your score for CS 101 Final is 42%.

要么

Your score for CS 101 Final is 42%.

或者对于这个：

Answer: 42

可不可能是

Answer 42

要么

Answer 42

(它只是一个键值对,因此定义列表不适用.)

我不仅仅想知道各个例子的正确标签.我想知道为什么他们是对的.我用什么标准来决定b或span标签？