对于搜索引擎来说，页面各个元素的权重比例。
Inbound link text: 10 points.
title: 10 points.
domain name: 7 points.
large h1-h2 headings: 5 points.
first sentence of first paragraph: 5 points.
path or filename: 4 points.
proximity (multi kws): 4 points.
beginning of a sentence 1.5 points.
bold or italic text: 1 point.
usage in text: 1 point.
title attribute: 1 point.
alt tag: .5 point.
meta descrip: .5 point.
meta keywords: .05 point.
