选择器 
    1    类型选择符               body{}
    2    群组选择符                h1,h2,h3,span{}
    3    包含选择符                h1 span{}
    4    id选择符                     #content{}
    5    class选择符                 .p1{}
    6    标签指定选择符         h1#content{}    h1.p1{}

伪类及伪对象
    1    伪类        :link:hover:active:visited:focus:first-child:first
    2    伪对象     :before    :after    :first-letter    :first-line 

xhtml对象类型
    1    block块状对象                占据一行
    2    in-line行间对象               可共享一行

xhtm标签
    结构标签        html,head,body,div,span
    Meta信息        DOCTYE,title,link,meta,vstyle
    文本控制        p,h1-h6,strong,abbr,acronym,address,bdo,blockquote,cite,q
    列表                ul,ol,li,dl,dt,dd
    表格                table,tr,td,th,tbody,thead,tfoot,col,colgroup,caption
    表单                form,input,textarea,select,option,optgroup,code,ins,del,dfn,kbd,pre,samp,var,br
    链接                a,vbase
    图像和对象    img,area,map,object,param
    脚本                script,noscript
    表现                b,i,tt,sub,sup,big,small,hr