No more undefined content in link and category

It seems that undefined content is only mentioned in RFC4287 because
link and category are elements and those usually need some content.

category.go

@@ -8,21 +8,14 @@ import (
 
 type Category struct {
 	*CommonAttributes
-	Content string `xml:",chardata"` // undefinedContent in RFC4287
-	Term    string `xml:"term,attr"`
-	Scheme  IRI    `xml:"scheme,attr,omitempty"`
-	Label   string `xml:"label,attr,omitempty"`
+	Term   string `xml:"term,attr"`
+	Scheme IRI    `xml:"scheme,attr,omitempty"`
+	Label  string `xml:"label,attr,omitempty"`
 }
 
 // NewCategory creates a new Category. It returns a *Category and an error.
-func NewCategory(term, content string) (*Category, error) {
-	if content != "" {
-		if !isValidXML(content) {
-			return nil, fmt.Errorf("%v not valid XML", content)
-		}
-	}
-
-	return &Category{Term: term, Content: content}, nil
+func NewCategory(term string) *Category {
+	return &Category{Term: term}
 }
 
 // SetLabel sets the label of the Category.
@@ -47,11 +40,5 @@ func (c *Category) Check() error {
 		return fmt.Errorf("label attribute %v of category not correctly escaped", c.Label)
 	}
 
-	if c.Content != "" {
-		if !isValidXML(c.Content) {
-			return fmt.Errorf("content element %v of category not valid XML", c.Content)
-		}
-	}
-
 	return nil
 }