prefixes

Returns an array of Strings containing all of the prefixes declared by this set of # attributes. The array does not include the default namespace declaration, if one exists.

doc = Document.new("<a xmlns='foo' xmlns:x='bar' xmlns:y='twee' "+
      "z='glorp' p:k='gru'/>")
prefixes = doc.root.attributes.prefixes    #-> ['x', 'y']