xml中的代码：
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE CATALOG SYSTEM "4.DTD">
<CATALOG>
<PRODUCT NAME="ff" >
<SPECIFICATIONS WEIGHT="1221" POWER="DSDS"></SPECIFICATIONS>
<OPRIONS></OPRIONS>
<PRICE/>
<NOTES/>
</PRODUCT>
</CATALOG>
4.DTD中的代码：
<?xml version="1.0" encoding="utf-8"?>
<!ELEMENT CATALOG (PRODUCT+)>
<!ELEMENT PRODUCT
(SPECIFICATIONS+,OPTIONS?,PRICE+,NOTES?)>
<!ATTLIST PRODUCT
NAME CDATA #IMPLIED
CATEGORY (HandTool|Table|Shop-Professional) "HandTool"
PARTNUM CDATA #IMPLIED
PLANT (Pittsburgh|Milwaukee|Chicago) "Chicago"
INVENTORY (InStock|Backordered|Discontinued) "InStock">
<!ELEMENT SPECIFICATIONS (#PCDATA)>
<!ATTLIST SPECIFICATIONS
WEIGHT CDATA #IMPLIED
POWER CDATA #IMPLIED>
<!ELEMENT OPTIONS (#PCDATA)>
<!ATTLIST OPTIONS
FINISH (Metal|Polished|Matte) "Matte"
ADAPTER (Included|Optional|NotApplicable) "Included"
CASE (HardShell|Soft|NotApplicable) "HardShell">
<!ELEMENT PRICE (#PCDATA)>
<!ELEMENT NOTES (#PCDATA)>
浏览器中效果：
<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE CATALOG (View Source for full doctype...)>
- <CATALOG>
- <PRODUCT NAME="ff" CATEGORY="HandTool" PLANT="Chicago" INVENTORY="InStock">
<SPECIFICATIONS WEIGHT="1221" POWER="DSDS" />
<OPRIONS />
<PRICE />
<NOTES />
</PRODUCT>
</CATALOG>
问题：PRODUCT中定义为DefaultValue的属性有显示出来，而OPRIONS中定义为DefaultValue的属性却没有显示出来？