foaf:birthday leaf node

@prefix foaf: <http://xmlns.com/foaf/0.1/> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix vs: <http://www.w3.org/2003/06/sw-vocab-status/ns#> .

foaf:birthday a rdf:Property,
        owl:DatatypeProperty,
        owl:FunctionalProperty ;
    rdfs:label "birthday" ;
    rdfs:comment "The birthday of this Agent, represented in mm-dd string form, eg. '12-31'." ;
    rdfs:domain foaf:Agent ;
    rdfs:isDefinedBy foaf: ;
    rdfs:range rdfs:Literal ;
    vs:term_status "unstable" .