XML_XRD is a PHP library to parse and generate Extensible Resource Descriptor (XRD) Version 1.0 files. The package parses XML XRD files and generates both XML and JSON (JRD) files.

XRD files are used for .well-known/host-meta files as standardized in RFC 6415: Web Host Metadata as well as in the LRDD (Link-based Resource Descriptor Discovery) files linked from it.

The LRDD XRD files can be used to discover information about users by just their e-mail address, e.g. the OpenID provider. This is the foundation of WebFinger, which lets people use their e-mail address to do OpenID sign in.

The XRD format supercedes the XRDS format defined in XRI 2.0, which is used in the Yadis communications protocol.