Force undefined content of category and link to be empty or valid xml

category.go

@@ -16,6 +16,10 @@ type Category struct {
 
 // NewCategory creates a new Category. It returns a *Category and an error.
 func NewCategory(term, content string) (*Category, error) {
+	if !isValidXML(content) {
+		return nil, fmt.Errorf("%v not valid XML", content)
+	}
+
 	return &Category{Term: term, Content: content}, nil
 }
 
@@ -41,8 +45,10 @@ func (c *Category) Check() error {
 		return fmt.Errorf("label attribute %v of category not correctly escaped", c.Label)
 	}
 
-	if c.Content == "" {
-		return errors.New("content element of category empty")
+	if c.Content != "" {
+		if !isValidXML(c.Content) {
+			return fmt.Errorf("content element %v of category not valid XML", c.Content)
+		}
 	}
 
 	return nil