XMDP

XHTML Meta Data Profiles (XMDP) is a format for defining metadata 'profiles' or formats in a machine-readable fashion, while also enabling people to see a description of the definition visually in a web browser. XMDP definitions are expressed in XHTML (or possibly HTML). Examples of applications that use XMDP include XFN and hCard.

Example
To apply, use the profile attribute in the head element of your document:

Where URL denotes the full address of your XMDP profile resource.