if(document.all)
document.write(""+"<frameset cols=210,* frameborder=NO border=0 framespacing=0 name=forum rows=*>"+
"<frame name=leftFrame frameborder=no src=xsleft_js.aspx scrolling=no noresize marginwidth=0 marginheight=0>");
else
document.write(""+"<frameset cols=210,* frameborder=NO border=0 framespacing=0 name=forum rows=*>"+
"<frame name=leftFrame frameborder=no src=left.aspx scrolling=no noresize marginwidth=0 marginheight=0>");
document.write(""+"<frame name=mainFrame scrolling=yes bordercolor=#6699cc style=BORDER-LEFT: #99ccff 2px groove; BORDER-TOP: #003366 1px solid>");
document.write(""+"</frameset>");
document.write(""+"<frame name=bottomFrame scrolling=NO noresize src=Bottom.aspx>");
document.write(""+"</frameset>");
这里的if语句是什么意思啊
------解决方案--------------------------------------------------------
document.all可以判断浏览器是否是IE