Add comments to author checks

entry.go

@@ -27,6 +27,10 @@ type Entry struct {
 	Extensions   []*ExtensionElement `xml:",any,omitempty"`
 }
 
+// atom:entry elements MUST contain one or more atom:author elements, unless
+// the atom:entry contains an atom:source element that contains an atom:author
+// element or, in an Atom Feed Document, the atom:feed element contains an
+// atom:author element itself.
 func (e *Entry) checkAuthors() error {
 	if e.Authors == nil {
 		if e.Source.Authors == nil {

feed.go

@@ -142,6 +142,9 @@ func (f *Feed) Check() error {
 		}
 	}
 
+	// atom:feed elements MUST contain one or more atom:author elements, unless
+	// all of the atom:feed element's child atom:entry elements contain at
+	// least one atom:author element.
 	if f.Authors == nil {
 		for _, e := range f.Entries {
 			if err := e.checkAuthors(); err != nil {