Unify error messages

outOfLineContent.go

@@ -2,7 +2,6 @@ package atom
 
 import (
 	"encoding/xml"
-	"errors"
 	"fmt"
 	"mime"
 )
@@ -27,7 +26,7 @@ func newOutOfLineContent(mediaType string, content any) (*OutOfLineContent, erro
 	}
 
 	if !isValidIRI(iri) {
-		return nil, errors.New("content not a valid uri")
+		return nil, fmt.Errorf("content %v not a valid uri", iri)
 	}
 
 	return &OutOfLineContent{Type: MediaType(mediaType), SRC: iri}, nil
@@ -54,11 +53,11 @@ func (o *OutOfLineContent) Check() error {
 	}
 
 	if isCompositeMediaType(mediaType) {
-		return errors.New("type attribute of out of line content must not be a composite type")
+		return fmt.Errorf("type attribute of out of line content %v must not be a composite type", o)
 	}
 
 	if o.SRC == "" {
-		return errors.New("src attribute of out of line content empty")
+		return fmt.Errorf("src attribute of out of line content %v empty", o)
 	}
 
 	return nil