1. Child Selector
 
H1 > Strong {color:red} is invalid,
 
Only H1 strong {color:red} can be used.
 
Child selectors are not supported, but derivation selectors are supported.
 
2.sibling Selector
 
Li+li {Font-style:bold} is not valid.
 
3.pseudo-class Selector Limited support.
 
a:link:visited {color: #fff;}, only the last one: visited.
 
It is best to write in the following order:
 
a:link {color:navy;}
 
a:visited {Color:gray;}
 
a:hover {color:red;}
 
a:active {color:yellow;}
 
IE6 is supported on pseudo class selectors and is limited to hyper-chain.
 
4 attribute Selector
 
H1[class] {color:silver;} is invalid.
 
The above is not supported, Eric Meyer's CSS authoritative guide points out that I have also been validated in the mainstream environment, IE6 Sp1/win XP.
 
5. But Eric Meyer's book says that IE does not support multiple-class selectors incorrectly, at least for IE6.
 
. warning.urgent {Background:silver} is valid, not invalid.