  <xs:element name="gwcConfiguration">
    <xs:complexType>
      <xs:sequence>
        ...
        <xs:element name="formatModifiers" type="gwc:formatModifiers" minOccurs="0">...</xs:element>
        
        <xs:element name="blobStores" minOccurs="0" maxOccurs="1">
          <xs:annotation>
            <xs:documentation xml:lang="en">
              The list of  blob stores. BlobStores allow to define a storage mechanism and format, such as the legacy file system
              based storage, an Amazon S3 instance with a TMS-like key structure, etc; independently of where the tiles come from
              in the TileLayer configuration. 
            </xs:documentation>
          </xs:annotation>
          <xs:complexType>
            <xs:sequence>
              <xs:element ref="gwc:blobstore" minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>
          </xs:complexType>
        </xs:element>
        
        <xs:element name="gridSets" minOccurs="0">
        ...
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:complexType name="AbstractBlobStore" abstract="true">
    <xs:sequence>
      <xs:element name="id" minOccurs="1" maxOccurs="1" type="xs:string" nillable="false">
        <xs:annotation>
          <xs:documentation>
            A blob store must have a unique identifier assigned through this element, which can be referenced
            by any number of TileLayer's 'blobStoreId'.
          </xs:documentation>
        </xs:annotation>
      </xs:element>
      <xs:element name="enabled" minOccurs="0" maxOccurs="1" type="xs:boolean" default="true">
        <xs:annotation>
          <xs:documentation>
            Defines whether the blob store is enabled (true) or disabled (false). Attempting to use
            a TileLayer whose blob store is disabled will result in a runtime exception.
          </xs:documentation>
        </xs:annotation>
      </xs:element>
    </xs:sequence>
    <xs:attribute name="default" type="xs:boolean" default="false">
      <xs:annotation>
        <xs:documentation xml:lang="en">
          The default attribute can only be true for one of the configured blob stores.
          If no blob store is configured as the default one, then one will be created automatically
          following the legacy location discovery method of looking for the GEOWEBCACHE_CACHE_DIR environment
          variable, servlet context parameter, or JVM argument.
          Additionally, any layer that has no blobStoreId set will default to use the default blob store,
          whether it is defined in the configuration file, or created automatically using the legacy method.
          So, it is allowed that none of the configured blob stores has its 'default' attribute set to true,
          but it's a configuration error that more than one is set as the default one. In such case, an exception
          will be thrown at application startup.
        </xs:documentation>
      </xs:annotation>
    </xs:attribute>
  </xs:complexType>
  
  <xs:element name="blobstore" type="gwc:AbstractBlobStore">
  </xs:element>
  
  <xs:element name="FileBlobStore" substitutionGroup="gwc:blobstore">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="gwc:AbstractBlobStore">
          <xs:sequence>
            <xs:element name="baseDirectory" type="xs:string" minOccurs="1" maxOccurs="1">
              
            </xs:element>
            <xs:element name="fileSystemBlockSize" type="xs:positiveInteger" minOccurs="0" maxOccurs="1" nillable="true">
            </xs:element>
          </xs:sequence>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
  
  <xs:element name="S3BlobStore" substitutionGroup="gwc:blobstore">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base="gwc:AbstractBlobStore">
          <xs:sequence>
            <xs:element name="bucket" type="xs:string" minOccurs="1">
              <xs:annotation>
                <xs:documentation xml:lang="en">the name of the AWS S3 bucket where to store tiles</xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="prefix" type="xs:string" minOccurs="0" nillable="true">
              <xs:annotation>
                <xs:documentation xml:lang="en">
                An optional prefix path to use as the "root folder" to store tiles at.
                For example, if the bucket is bucket.gwc.example and prefix is "mycache", all tiles will be stored under
                bucket.gwc.example/mycache/{layer name} instead of bucket.gwc.example/{layer name}.
                </xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="awsAccessKey" type="xs:string" minOccurs="1">
              <xs:annotation>
                <xs:documentation xml:lang="en">The public access key the client uses to connect to S3.</xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="awsSecretKey" type="xs:string" minOccurs="1">
              <xs:annotation>
                <xs:documentation xml:lang="en">The secret key the client uses to connect to S3</xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="maxConnections" type="xs:positiveInteger" minOccurs="0" default="50" nillable="true">
              <xs:annotation>
                <xs:documentation xml:lang="en">Maximum number of concurrent HTTP connections the S3 client may use.</xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="useHTTPS" type="xs:boolean" minOccurs="0" default="true" nillable="true">
              <xs:annotation>
                <xs:documentation xml:lang="en">Whether to use HTTPS when connecting to S3 or not</xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="proxyDomain" type="xs:string" minOccurs="0" nillable="true">
              <xs:annotation>
                <xs:documentation xml:lang="en">
                The optional Windows domain name for configuring an NTLM proxy.
                If you aren't using a Windows NTLM proxy, you do not need to set this field. 
                </xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="proxyWorkstation" type="xs:string" minOccurs="0" nillable="true">
              <xs:annotation>
                <xs:documentation xml:lang="en">
                The optional Windows workstation name for configuring NTLM proxy support. 
                If you aren't using a Windows NTLM proxy, you do not need to set this field.
                </xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="proxyHost" type="xs:string" minOccurs="0" nillable="true">
              <xs:annotation>
                <xs:documentation xml:lang="en">The optional proxy host the client will connect through.</xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="proxyPort" type="xs:positiveInteger" minOccurs="0" nillable="true">
              <xs:annotation>
                <xs:documentation xml:lang="en">The optional proxy port the client will connect through.</xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="proxyUsername" type="xs:string" minOccurs="0" nillable="true">
              <xs:annotation>
                <xs:documentation xml:lang="en">The optional proxy user name to use if connecting through a proxy.</xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="proxyPassword" type="xs:string" minOccurs="0" nillable="true">
              <xs:annotation>
                <xs:documentation xml:lang="en">The optional proxy password to use when connecting through a proxy.</xs:documentation>
              </xs:annotation>
            </xs:element>
            <xs:element name="useGzip" type="xs:boolean" minOccurs="0" default="false" nillable="true">
              <xs:annotation>
                <xs:documentation xml:lang="en">Whether gzip compression should be used.</xs:documentation>
              </xs:annotation>
            </xs:element>
          </xs:sequence>
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
...