当有例如PHP/cURL时,crossdomain.xml和clientaccesspolicy.xml的含义是什么？

<?xml version="1.0"?>
<!DOCTYPE cross-domain-policy SYSTEM "http://www.adobe.com/xml/dtds/cross-domain-policy.dtd"><cross-domain-policy>
  <site-control permitted-cross-domain-policies="all"/>
 <allow-access-from domain="*" secure="false"/>
 <allow-http-request-headers-from domain="*" headers="*"/>
</cross-domain-policy>

<?xml version="1.0" encoding="utf-8"?><access-policy>
 <cross-domain-access>
   <policy>
     <allow-from http-request-headers="*">
       <domain uri="*"/>
      </allow-from>
      <grant-to>
       <resource path="/" include-subpaths="true"/>
      </grant-to>
    </policy>
  </cross-domain-access>
</access-policy>