xmlns是什么意思
我看见下面几行代码:<xbrl xmlns="http://www.xbrl.org/2003/instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" >
<link:schemaRefxlink:type="simple" xlink:href="http://www.xbrl-cn.org/cn/lcid/ci/qr/2006-03-31/clcid-ci-qr-2006-03-31.xsd" />
</xbrl>
我想问一下xmlns="http://www.xbrl.org/2003/instance和<link:schemaRefxlink:type="simple" xlink:href="http://www.xbrl-cn.org/cn/lcid/ci/qr/2006-03-31/clcid-ci-qr-2006-03-31.xsd" />这两句代码是什么含义