選擇器 
    1    類型選擇符               body{}
    2    群組選擇符                h1,h2,h3,span{}
    3    包含選擇符                h1 span{}
    4    id選擇符                     #content{}
    5    class選擇符                 .p1{}
    6    標簽指定選擇符         h1#content{}    h1.p1{}

偽類及偽對象
    1    偽類        :link:hover:active:visited:focus:first-child:first
    2    偽對象     :before    :after    :first-letter    :first-line 

xhtml對象類型
    1    block塊狀對象                占據(jù)一行
    2    in-line行間對象               可共享一行

xhtm標簽
    結(jié)構(gòu)標簽        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
    表單                form,input,textarea,select,option,optgroup,code,ins,del,dfn,kbd,pre,samp,var,br
    鏈接                a,vbase
    圖像和對象    img,area,map,object,param
    腳本                script,noscript
    表現(xiàn)                b,i,tt,sub,sup,big,small,hr