Added and corrected comments

atom.go

@@ -31,14 +31,16 @@ type (
 // 	return isValidURL(uri) || isValidURN(uri)
 // }
 
-// isValidIRI checks whether an IRI is valid or not.
+// isValidIRI checks whether an IRI is valid or not. It returns a bool.
 // The used pattern stems from
-// https://www.w3.org/2011/04/XMLSchema/TypeLibrary-IRI-RFC3987.xsd
+// https://www.w3.org/2011/04/XMLSchema/TypeLibrary-IRI-RFC3987.xsd.
 func isValidIRI(iri IRI) bool {
 	pattern := `((([A-Za-z])[A-Za-z0-9+\-\.]*):((//(((([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽!$&'()*+,;=:]|(%[0-9A-Fa-f][0-9A-Fa-f]))*@))?((\[((((([0-9A-Fa-f]{0,4}:)){6}(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|(::(([0-9A-Fa-f]{0,4}:)){5}(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|(([0-9A-Fa-f]{0,4})?::(([0-9A-Fa-f]{0,4}:)){4}(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|((((([0-9A-Fa-f]{0,4}:))?[0-9A-Fa-f]{0,4}))?::(([0-9A-Fa-f]{0,4}:)){3}(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|((((([0-9A-Fa-f]{0,4}:)){0,2}[0-9A-Fa-f]{0,4}))?::(([0-9A-Fa-f]{0,4}:)){2}(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|((((([0-9A-Fa-f]{0,4}:)){0,3}[0-9A-Fa-f]{0,4}))?::[0-9A-Fa-f]{0,4}:(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|((((([0-9A-Fa-f]{0,4}:)){0,4}[0-9A-Fa-f]{0,4}))?::(([0-9A-Fa-f]{0,4}:[0-9A-Fa-f]{0,4})|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))))|((((([0-9A-Fa-f]{0,4}:)){0,5}[0-9A-Fa-f]{0,4}))?::[0-9A-Fa-f]{0,4})|((((([0-9A-Fa-f]{0,4}:)){0,6}[0-9A-Fa-f]{0,4}))?::))|(v[0-9A-Fa-f]+\.[A-Za-z0-9\-\._~!$&'()*+,;=:]+))\])|(([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5]))\.([0-9]|([1-9][0-9])|(1([0-9]){2})|(2[0-4][0-9])|(25[0-5])))|(([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=]))*)((:[0-9]*))?)((/(([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@]))*))*)|(/(((([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@]))+((/(([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@]))*))*))?)|((([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@]))+((/(([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@]))*))*)|)((\?(([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@])|[-󰀀-󿿽􀀀-􏿽/?])*))?((#((([A-Za-z0-9\-\._~ -퟿豈-﷏ﷰ-￯𐀀-🿽𠀀-𯿽𰀀-𿿽񀀀-񏿽񐀀-񟿽񠀀-񯿽񰀀-񿿽򀀀-򏿽򐀀-򟿽򠀀-򯿽򰀀-򿿽󀀀-󏿽󐀀-󟿽󡀀-󯿽]|(%[0-9A-Fa-f][0-9A-Fa-f])|[!$&'()*+,;=:@])|/|\?))*))?)`
 	return regexp.MustCompile(pattern).MatchString(string(iri))
 }
 
+// isCorrectlyEscaped checks whether a string is correctly escaped as per
+// RFC4287. It returns a bool.
 func isCorrectlyEscaped(text string) bool {
 	relevantEntities := []string{"&", "<", ">", """, "'"}
 
@@ -51,6 +53,8 @@ func isCorrectlyEscaped(text string) bool {
 	return true
 }
 
+// isCompositeMediaType checks whether a string is a composite media type. It
+// returns a bool.
 func isCompositeMediaType(mediaType string) bool {
 	mediaType, _, err := mime.ParseMediaType(mediaType)
 	if err != nil {
@@ -60,6 +64,8 @@ func isCompositeMediaType(mediaType string) bool {
 	return strings.HasPrefix(mediaType, "multipart/") || strings.HasPrefix(mediaType, "message/")
 }
 
+// isXMLMediaType checks whether a string is an xml media type. It returns a
+// bool.
 func isXMLMediaType(mediaType string) bool {
 	mediaType, _, err := mime.ParseMediaType(mediaType)
 	if err != nil {
@@ -69,11 +75,14 @@ func isXMLMediaType(mediaType string) bool {
 	return strings.HasSuffix(mediaType, "/xml") || strings.HasSuffix(mediaType, "+xml")
 }
 
+// isValidMediaType checks whether a string is a valid media type. It returns a
+// bool.
 func isValidMediaType(mediaType string) bool {
 	_, _, err := mime.ParseMediaType(mediaType)
 	return err == nil
 }
 
+// isValidLanguageTag checks whether a LanguageTag is valid. It returns a bool.
 func isValidLanguageTag(tag LanguageTag) bool {
 	_, err := language.Parse(string(tag))
 	return err == nil

category.go

@@ -14,6 +14,7 @@ type Category struct {
 	Label   string  `xml:"label,attr,omitempty"`
 }
 
+// NewCategory creates a new Category. It returns a *Category and an error.
 func NewCategory(term string) (*Category, error) {
 	content, err := NewContent(InlineText, "", "")
 	if err != nil {
@@ -23,10 +24,13 @@ func NewCategory(term string) (*Category, error) {
 	return &Category{Term: term, Content: content}, nil
 }
 
+// SetLabel sets the label of the Category.
 func (c *Category) SetLabel(label string) {
 	c.Label = html.UnescapeString(label)
 }
 
+// Check checks the Category for incompatibilities with RFC4287. It returns an
+// error.
 func (c *Category) Check() error {
 	if c.Term == "" {
 		return errors.New("term attribute of category empty")

commonAttributes.go

@@ -8,6 +8,8 @@ type CommonAttributes struct {
 	UndefinedAttributes []*ExtensionAttribute `xml:",any"`
 }
 
+// Check checks the CommonAttributes for incompatibilities with RFC4287. It
+// returns an error.
 func (c *CommonAttributes) Check() error {
 	for i, e := range c.UndefinedAttributes {
 		if err := e.Check(); err != nil {

content.go

@@ -18,6 +18,7 @@ type Content interface {
 	Check() error
 }
 
+// NewContent creates a new Content. It returns a Content and an error.
 func NewContent(contentType int, mediaType string, content any) (Content, error) {
 	switch contentType {
 	case 0:

date.go

@@ -10,14 +10,19 @@ type Date struct {
 	DateTime string
 }
 
+// DateTime formats a time.Time to string formated as defined by RFC3339. It
+// returns a string.
 func DateTime(t time.Time) string {
 	return string(t.Format(time.RFC3339))
 }
 
+// NewDate creates a new Date. It returns a *Date.
 func NewDate(t time.Time) *Date {
 	return &Date{DateTime: DateTime(t)}
 }
 
+// Check checks the Date for incompatibilities with RFC4287. It returns an
+// error.
 func (d *Date) Check() error {
 	if d.DateTime == "" {
 		return errors.New("date time element of date is empty")

entry.go

@@ -28,6 +28,8 @@ type Entry struct {
 	Extensions   []*ExtensionElement `xml:",any,omitempty"`
 }
 
+// checkAuthors checks the entry's authors for incompatibilities with RFC4287.
+// It returns an errors.
 // 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
@@ -48,17 +50,21 @@ func (e *Entry) checkAuthors() error {
 	return nil
 }
 
-func alternateRelExists(l []*Link) bool {
+// NewEntry creates a new Entry. It returns a *Entry and an error.
-	for _, link := range l {
+func NewEntry(title string) (*Entry, error) {
-		if link.Rel == "alternate" {
+	text, err := NewText("text", title)
-			return true
+	if err != nil {
-		}
+		return nil, fmt.Errorf("error creating new entry: %v", err)
 	}
 
-	return false
+	return &Entry{
+		ID:      NewID(),
+		Title:   text,
+		Updated: NewDate(time.Now()),
+	}, nil
 }
 
-// AddExtension adds the extension to the entry
+// AddExtension adds the ExtensionElement to the Entry.
 func (e *Entry) AddExtension(x *ExtensionElement) {
 	if e.Extensions == nil {
 		e.Extensions = make([]*ExtensionElement, 1)
@@ -70,6 +76,8 @@ func (e *Entry) AddExtension(x *ExtensionElement) {
 	e.Updated.DateTime = DateTime(time.Now())
 }
 
+// Check checks the Entry for incompatibilities with RFC4287. It returns an
+// error.
 func (e *Entry) Check() error {
 	if e.ID == nil {
 		return errors.New("no id element of entry")

extensionAttribute.go

@@ -10,6 +10,8 @@ type ExtensionAttribute struct {
 	XMLName xml.Name
 }
 
+// Check checks the ExtensionAttribute for incompatibilities with RFC4287. It
+// returns an error.
 func (e *ExtensionAttribute) Check() error {
 	if e.Value == nil {
 		return errors.New("value element of extension attribute empty")

extensionElement.go

@@ -10,10 +10,14 @@ type ExtensionElement struct {
 	XMLName xml.Name
 }
 
+// NewExtensionElement creates a new ExtensionElement. It returns a
+// *ExtensionElement.
 func NewExtensionElement(name string, value any) *ExtensionElement {
 	return &ExtensionElement{XMLName: xml.Name{Local: name}, Value: value}
 }
 
+// Check checks the ExtensionElement for incompatibilities with RFC4287. It
+// returns an error.
 func (e *ExtensionElement) Check() error {
 	if e.Value == nil {
 		return errors.New("value element of extension element empty")

feed.go

@@ -26,7 +26,7 @@ type Feed struct {
 	Entries      []*Entry            `xml:"entry,omitempty"`
 }
 
-// NewFeed creates a new feed.
+// NewFeed creates a new Feed. It returns a *Feed and an error.
 func NewFeed(title string) (*Feed, error) {
 	text, err := NewText("text", title)
 	if err != nil {
@@ -40,7 +40,7 @@ func NewFeed(title string) (*Feed, error) {
 	}, nil
 }
 
-// AddAuthor adds the person as an author to the feed.
+// AddAuthor adds the Person as an author to the Feed.
 func (f *Feed) AddAuthor(p *Person) {
 	if f.Authors == nil {
 		f.Authors = make([]*Person, 1)
@@ -52,7 +52,7 @@ func (f *Feed) AddAuthor(p *Person) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// AddCategory adds the category to the feed.
+// AddCategory adds the Category to the Feed.
 func (f *Feed) AddCategory(c *Category) {
 	if f.Categories == nil {
 		f.Categories = make([]*Category, 1)
@@ -64,7 +64,7 @@ func (f *Feed) AddCategory(c *Category) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// AddContributor adds the contributor to the feed.
+// AddContributor adds the Person as a contributor to the Feed.
 func (f *Feed) AddContributor(c *Person) {
 	if f.Contributors == nil {
 		f.Contributors = make([]*Person, 1)
@@ -76,8 +76,7 @@ func (f *Feed) AddContributor(c *Person) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// AddLink adds the link to the feed.
+// AddLink adds the Link to the Feed. There should be one Link with Rel "self".
-// There should be one link with rel "self".
 func (f *Feed) AddLink(l *Link) {
 	if f.Links == nil {
 		f.Links = make([]*Link, 1)
@@ -89,7 +88,7 @@ func (f *Feed) AddLink(l *Link) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// AddExtension adds the extension to the feed.
+// AddExtension adds the Extension to the Feed.
 func (f *Feed) AddExtension(e *ExtensionElement) {
 	if f.Extensions == nil {
 		f.Extensions = make([]*ExtensionElement, 1)
@@ -101,7 +100,7 @@ func (f *Feed) AddExtension(e *ExtensionElement) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// AddEntry adds the entry to the feed.
+// AddEntry adds the Entry to the Feed.
 func (f *Feed) AddEntry(e *Entry) {
 	if f.Entries == nil {
 		f.Entries = make([]*Entry, 1)
@@ -113,7 +112,8 @@ func (f *Feed) AddEntry(e *Entry) {
 	f.Updated.DateTime = DateTime(time.Now())
 }
 
-// Check checks the feed for incompatibilities with RFC4287.
+// Check checks the Feed for incompatibilities with RFC4287. It returns an
+// error.
 func (f *Feed) Check() error {
 	if f.ID == nil {
 		return errors.New("no id element of feed")
@@ -222,26 +222,7 @@ func (f *Feed) Check() error {
 	return nil
 }
 
-// TODO: Create complete link or delete
+// ToXML converts the Feed to XML. It returns a string and an error.
-func (f *Feed) Standardize() {
-	if f.Links == nil {
-		f.Links = make([]*Link, 1)
-		f.Links[0] = &Link{Rel: "self"}
-	} else {
-		selfExists := false
-		for _, l := range f.Links {
-			if l.Rel == "self" {
-				selfExists = true
-				break
-			}
-		}
-		if !selfExists {
-			f.Links = append(f.Links, &Link{Rel: "self"})
-		}
-	}
-}
-
-// ToXML converts the feed to XML.
 func (f *Feed) ToXML(encoding string) (string, error) {
 	xml, err := xml.MarshalIndent(f, "", "  ")
 	if err != nil {

generator.go

@@ -13,10 +13,13 @@ type Generator struct {
 	Text    string `xml:"text"`
 }
 
+// NewGenerator creates a new Generator. It returns a *Generator.
 func NewGenerator(text string) *Generator {
 	return &Generator{Text: html.UnescapeString(text)}
 }
 
+// Check checks the Generator for incompatibilities with RFC4287. It returns an
+// error.
 func (g *Generator) Check() error {
 	if g.URI != "" {
 		if !isValidIRI(g.URI) {

icon.go

@@ -10,10 +10,13 @@ type Icon struct {
 	URI IRI `xml:"uri"`
 }
 
+// NewIcon creates a new Icon. It returns a *Icon.
 func NewIcon(uri string) *Icon {
 	return &Icon{URI: IRI(uri)}
 }
 
+// Check checks the Icon for incompatibilities with RFC4287. It returns an
+// error.
 func (i *Icon) Check() error {
 	if i.URI == "" {
 		return errors.New("uri element of icon empty")

id.go

@@ -12,10 +12,12 @@ type ID struct {
 	URI IRI `xml:"uri"`
 }
 
+// NewID creates a new ID. It returns a *ID.
 func NewID() *ID {
 	return &ID{URI: IRI(fmt.Sprint("urn:uuid:", uuid.New()))}
 }
 
+// Check checks the ID for incompatibilities with RFC4287. It returns an error.
 func (i *ID) Check() error {
 	if i.URI == "" {
 		return errors.New("uri element of id empty")

inlineOtherContent.go

@@ -12,6 +12,8 @@ type InlineOtherContent struct {
 	Type       MediaType `xml:"type,attr,omitempty"`
 }
 
+// newInlineOtherContent creates a new InlineOtherContent. It returns a
+// *InlineOtherContent and an error.
 func newInlineOtherContent(mediaType string, content any) (*InlineOtherContent, error) {
 	if mediaType, _, err := mime.ParseMediaType(mediaType); err != nil {
 		return nil, fmt.Errorf("media type %v incompatible with inline other content", mediaType)
@@ -20,12 +22,19 @@ func newInlineOtherContent(mediaType string, content any) (*InlineOtherContent,
 	return &InlineOtherContent{Type: MediaType(mediaType), AnyElement: content}, nil
 }
 
+// isContent checks whether the InlineOtherContent is a Content. It returns a
+// bool.
 func (i *InlineOtherContent) isContent() bool { return true }
 
+// hasSRC checks whether the InlineOtherContent has a SRC attribute. It returns
+// a bool.
 func (i *InlineOtherContent) hasSRC() bool { return false }
 
+// getType returns the Type of the InlineOtherContent as a string.
 func (i *InlineOtherContent) getType() string { return string(i.Type) }
 
+// Check checks the InlineOtherContent for incompatibilities with RFC4287. It
+// returns an error.
 func (i *InlineOtherContent) Check() error {
 	mediaType := i.getType()
 

inlineTextContent.go

@@ -12,6 +12,8 @@ type InlineTextContent struct {
 	Texts []string `xml:"texts,omitempty"`
 }
 
+// newInlineTextContent creates a new InlineTextContent. It returns a
+// *InlineTextContent and an error.
 func newInlineTextContent(mediaType string, content any) (*InlineTextContent, error) {
 	if mediaType != "text" && mediaType != "html" && mediaType != "" {
 		return nil, fmt.Errorf("media type %v incompatible with inline text content", mediaType)
@@ -36,12 +38,19 @@ func newInlineTextContent(mediaType string, content any) (*InlineTextContent, er
 	return &InlineTextContent{Type: mediaType, Texts: texts}, nil
 }
 
+// isContent checks whether the InlineTextContent is a Content. It returns a
+// bool.
 func (i *InlineTextContent) isContent() bool { return true }
 
+// hasSRC checks whether the InlineTextContent has a SRC attribute. It returns
+// a bool.
 func (i *InlineTextContent) hasSRC() bool { return false }
 
+// getType returns the Type of the InlineTextContent as a string.
 func (i *InlineTextContent) getType() string { return i.Type }
 
+// Check checks the InlineTextContent for incompatibilities with RFC4287. It
+// returns an error.
 func (i *InlineTextContent) Check() error {
 	if i.Type != "" && i.Type != "text" && i.Type != "html" {
 		return errors.New("type attribute of inline text content must be text or html if not omitted")

inlineXHTMLContent.go

@@ -12,6 +12,8 @@ type InlineXHTMLContent struct {
 	XHTMLDiv string `xml:"xhtmldiv"`
 }
 
+// newInlineXHTMLContent creates a new InlineXHTMLContent. It returns a
+// *InlineXHTMLContent and an error.
 func newInlineXHTMLContent(mediaType string, content any) (*InlineXHTMLContent, error) {
 	if mediaType != "xhtml" {
 		return nil, fmt.Errorf("media type %v incompatible with inline xhtml content", mediaType)
@@ -24,12 +26,19 @@ func newInlineXHTMLContent(mediaType string, content any) (*InlineXHTMLContent,
 	return &InlineXHTMLContent{Type: mediaType, XHTMLDiv: content.(string)}, nil
 }
 
+// isContent checks whether the InlineXHTMLContent is a Content. It returns a
+// bool.
 func (i *InlineXHTMLContent) isContent() bool { return true }
 
+// hasSRC checks whether the InlineXHTMLContent has a SRC attribute. It returns
+// a bool.
 func (i *InlineXHTMLContent) hasSRC() bool { return false }
 
+// getType returns the Type of the InlineXHTMLContent as a string.
 func (i *InlineXHTMLContent) getType() string { return i.Type }
 
+// Check checks the InlineXHTMLContent for incompatibilities with RFC4287. It
+// returns an error.
 func (i *InlineXHTMLContent) Check() error {
 	if i.Type != "xhtml" {
 		return errors.New("type attribute of inline xhtml content must be xhtml")

link.go

@@ -17,6 +17,7 @@ type Link struct {
 	Length   uint        `xml:"length,attr,omitempty"`
 }
 
+// NewLink creates a new Link. It returns a *Link and an error.
 func NewLink(href string) (*Link, error) {
 	content, err := NewContent(InlineText, "", "")
 	if err != nil {
@@ -26,6 +27,8 @@ func NewLink(href string) (*Link, error) {
 	return &Link{Href: IRI(href), Content: content}, nil
 }
 
+// Check checks the Link for incompatibilities with RFC4287. It returns an
+// error.
 func (l *Link) Check() error {
 	if l.Href == "" {
 		return errors.New("href attribute of link empty")
@@ -58,6 +61,8 @@ func (l *Link) Check() error {
 	return nil
 }
 
+// hasAlternateDuplicateLinks checks whether multiple Links with Rel
+// "alternate" also have Type and HrefLang in common. It returns a bool.
 // atom:feed/entry elements MUST NOT contain more than one atom:link element
 // with a rel attribute value of "alternate" that has the same combination of
 // type and hreflang attribute values.
@@ -76,3 +81,15 @@ func hasAlternateDuplicateLinks(l []*Link) bool {
 
 	return false
 }
+
+// alternateRelExists checks whether multiple Links with Rel "alternate" exist.
+// It returns a bool.
+func alternateRelExists(l []*Link) bool {
+	for _, link := range l {
+		if link.Rel == "alternate" {
+			return true
+		}
+	}
+
+	return false
+}

logo.go

@@ -12,10 +12,13 @@ type Logo struct {
 	URI IRI `xml:"uri"`
 }
 
+// NewLogo creates a new Logo. It returns a *Logo.
 func NewLogo() *Logo {
 	return &Logo{URI: IRI(fmt.Sprint("urn:uuid:", uuid.New()))}
 }
 
+// Check checks the Logo for incompatibilities with RFC4287. It returns an
+// error.
 func (l *Logo) Check() error {
 	if l.URI == "" {
 		return errors.New("uri element of logo empty")

outOfLineContent.go

@@ -13,6 +13,8 @@ type OutOfLineContent struct {
 	SRC  IRI       `xml:"src,attr"`
 }
 
+// newOutOfLineContent creates a new OutOfLineContent. It returns a
+// *OutOfLineContent and an error.
 func newOutOfLineContent(mediaType string, content any) (*OutOfLineContent, error) {
 	if mediaType, _, err := mime.ParseMediaType(mediaType); err != nil {
 		return nil, fmt.Errorf("media type %v incompatible with out of line content", mediaType)
@@ -29,12 +31,19 @@ func newOutOfLineContent(mediaType string, content any) (*OutOfLineContent, erro
 	return &OutOfLineContent{Type: MediaType(mediaType), SRC: content.(IRI)}, nil
 }
 
+// isContent checks whether the OutOfLineContent is a Content. It returns a
+// bool.
 func (o *OutOfLineContent) isContent() bool { return true }
 
+// hasSRC checks whether the OutOfLineContent has a SRC attribute. It returns a
+// bool.
 func (o *OutOfLineContent) hasSRC() bool { return true }
 
+// getType returns the Type of the OutOfLineContent as a string.
 func (o *OutOfLineContent) getType() string { return string(o.Type) }
 
+// Check checks the OutOfLineContent for incompatibilities with RFC4287. It
+// returns an error.
 func (o *OutOfLineContent) Check() error {
 	mediaType := o.getType()
 

person.go

@@ -14,11 +14,12 @@ type Person struct {
 	Extensions []*ExtensionElement `xml:",any,omitempty"`
 }
 
+// NewPerson creates a new Person. It returns a *Person.
 func NewPerson(name string) *Person {
 	return &Person{Name: name}
 }
 
-// AddExtension adds the extension to the person
+// AddExtension adds the Extension to the Person.
 func (p *Person) AddExtension(e *ExtensionElement) {
 	if p.Extensions == nil {
 		p.Extensions = make([]*ExtensionElement, 1)
@@ -28,6 +29,8 @@ func (p *Person) AddExtension(e *ExtensionElement) {
 	}
 }
 
+// Check checks the Person for incompatibilities with RFC4287. It returns an
+// error.
 func (p *Person) Check() error {
 	if p.Name == "" {
 		return errors.New("name element of person element empty")

plainText.go

@@ -8,8 +8,11 @@ type PlainText struct {
 	Text string `xml:"text"`
 }
 
+// isText checks whether the PlainText is a Text. It returns a bool.
 func (p *PlainText) isText() bool { return true }
 
+// Check checks the PlainText for incompatibilities with RFC4287. It returns an
+// error.
 func (p *PlainText) Check() error {
 	if p.Type != "" && p.Type != "text" && p.Type != "html" {
 		return errors.New("type attribute of plain text must be text or html if not omitted")

source.go

@@ -19,6 +19,8 @@ type Source struct {
 	Extensions   []*ExtensionElement `xml:",any,omitempty"`
 }
 
+// Check checks the Source for incompatibilities with RFC4287. It returns an
+// error.
 func (s *Source) Check() error {
 	for i, a := range s.Authors {
 		if err := a.Check(); err != nil {

text.go

@@ -10,6 +10,7 @@ type Text interface {
 	Check() error
 }
 
+// NewText creates a new Text. It returns a Text and an error.
 func NewText(textType, content string) (Text, error) {
 	switch textType {
 	case "text", "":

xhtmlText.go

@@ -17,8 +17,11 @@ type XHTMLText struct {
 	XHTMLDiv XHTMLDiv
 }
 
+// isText checks whether the XHTMLText is a Text. It returns a bool.
 func (x *XHTMLText) isText() bool { return true }
 
+// Check checks the XHTMLText for incompatibilities with RFC4287. It returns an
+// error.
 func (x *XHTMLText) Check() error {
 	if x.Type != "xhtml" {
 		return errors.New("type attribute of xhtml text must be xhtml")