Purpose of defining an attribute globally in XSD

In XSD it is possible to define an attribute right under the schema element, like I have defined someAttr in the XSD below:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="http://www.example.com"
           xmlns:xs="http://www.w3.org/2001/XMLSchema" 
           elementFormDefault="qualified" 
           attributeFormDefault="unqualified">
    <xs:element name="Companys">
        <xs:annotation>
            <xs:documentation>Comment describing your root element</xs:documentation>
        </xs:annotation>
        <xs:complexType>
            <xs:sequence>
                <xs:element name="Company" maxOccurs="unbounded">
                    <xs:complexType>
                        <xs:attribute name="companyname" type="xs:string" default="test1"/>
                    </xs:complexType>
                </xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:attribute name="someAttr" type="xs:string" default="R"/>
</xs:schema>

How would you use it?

You would use it via xs:attribute/@ref, which is particularly handy to allow one definition of someAttr to be used in multiple locations.

XSD

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="http://www.example.com"
           xmlns:e="http://www.example.com"
           xmlns:xs="http://www.w3.org/2001/XMLSchema"
           elementFormDefault="qualified"
           attributeFormDefault="unqualified">
  <xs:element name="Companys">
    <xs:annotation>
      <xs:documentation>Comment describing your root element</xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:sequence>
        <xs:element name="Company" maxOccurs="unbounded">
          <xs:complexType>
            <xs:attribute name="companyname" type="xs:string" default="test1"/>
            <xs:attribute ref="e:someAttr"/>
          </xs:complexType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
  <xs:attribute name="someAttr" type="xs:string" default="R"/>
</xs:schema>