Check whether there is a link element with a rel attribute of "alternate" if there is no content element in an entry element

entry.go

@@ -43,6 +43,16 @@ func (e *Entry) checkAuthors() error {
 	return nil
 }
 
+func alternateRelExists(l []*Link) bool {
+	for _, link := range l {
+		if link.Rel == "alternate" {
+			return true
+		}
+	}
+
+	return false
+}
+
 func (e *Entry) AddExtension(name string, value any) {
 	e.Extensions = append(e.Extensions, &ExtensionElement{XMLName: xml.Name{Local: name}, Value: value})
 }
@@ -72,6 +82,10 @@ func (e *Entry) Check() error {
 		if err := (*e.Content).Check(); err != nil {
 			return fmt.Errorf("content element of entry %v: %v", e.ID.URI, err)
 		}
+	} else {
+		if !alternateRelExists(e.Links) {
+			return errors.New("no content element of entry %v and no link element with rel \"alternate\"")
+		}
 	}
 
 	if e.Contributors != nil {