<hr>文件头里没有写 xmlns:xsi、xsi:schemaLocation 这两句，IDEA为啥也能校验xsd文件？

<?xml version="1.0" encoding="utf-8" ?>
<!--文档类型使用xsd文件进行语义约束-->
<!--文档注释-->
<hr xmlns="http://www.given.com"
    >
    <employee no="3000">
        <name>张三</name>
        <age>18</age>
        <salary>10000</salary>
        <department>
            <dname>会计部</dname>
            <address>漳州市龙文区</address>
        </department>
    </employee>
    <employee no="3001">
        <name>李四</name>
        <age>19</age>
        <salary>5000</salary>
        <department>
            <dname>研发部</dname>
            <address>漳州市芗城区</address>
        </department>
    </employee>
</hr>

<schema xmlns="http://www.w3.org/2001/XMLSchema"
        targetNamespace="http://www.given.com"
        elementFormDefault="qualified"
>
    <element name="hr">
        <complexType>
            <sequence>
                <element name="employee" minOccurs="1" maxOccurs="9999">
                    <complexType>
                        <sequence>
                            <element name="name" type="string"></element>
                            <element name="age">
                                <simpleType>
                                    <restriction base="integer">
                                        <minInclusive value="18"></minInclusive>
                                        <maxInclusive value="65"></maxInclusive>
                                    </restriction>
                                </simpleType>
                            </element>
                            <element name="salary" type="integer"></element>
                            <element name="department">
                                <complexType>
                                    <sequence>
                                        <element name="dname" type="string"></element>
                                        <element name="address" type="string"></element>
                                    </sequence>
                                </complexType>
                            </element>
                        </sequence>
                        <attribute name="no" type="string" use="required"></attribute>
                    </complexType>
                </element>
            </sequence>
        </complexType>
    </element>
</schema>