Declaração de marcação externa DTD esperada [duplicado]

Question

Tenho um problema com a validação XML ao adicionar validação DTD externa. Isso funciona normalmente:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE booklist [
<!ELEMENT booklist (book)*>
<!ELEMENT book (author,title,published?)>
<!ELEMENT author (firstname,lastname)>
<!ELEMENT firstname (#PCDATA)>
<!ELEMENT lastname (#PCDATA)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT published (#PCDATA)>
<!ATTLIST book genre (Science|Fiction) #REQUIRED>
<!ATTLIST book format (Paperback|Hardcover) "Paperback">
]>
<booklist>
  <book genre="Fiction" format="Paperback">
    <author>
      <firstname>Name</firstname>
      <lastname>Surname</lastname>
    </author>
    <title>Sample</title>
    <published>2020</published>
  </book>
</booklist>

Quando tento adicionar uma declaração dtd externa, o editor de cópia XML gera um erro

Erro fatal na linha 1, coluna 3: declaração de marcação esperada

XML

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE booklist SYSTEM "booklist.dtd">
<booklist>
  <book genre="Fiction" format="Paperback">
    <author>
      <firstname>Name</firstname>
      <lastname>Surname</lastname>
    </author>
    <title>Sample</title>
    <published>2020</published>
  </book>
</booklist>

DTD

<!DOCTYPE booklist [
<!ELEMENT booklist (book)*>
<!ELEMENT book (author,title,published?)>
<!ELEMENT author (firstname,lastname)>
<!ELEMENT firstname (#PCDATA)>
<!ELEMENT lastname (#PCDATA)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT published (#PCDATA)>
<!ATTLIST book genre (Science|Fiction) #REQUIRED>
<!ATTLIST book format (Paperback|Hardcover) "Paperback">
]>

O que estou fazendo errado ?

Answer 1

Remova o DOCTYPEinvólucro do seu subconjunto externo:

DTD externo

<!ELEMENT booklist (book)*>
<!ELEMENT book (author,title,published?)>
<!ELEMENT author (firstname,lastname)>
<!ELEMENT firstname (#PCDATA)>
<!ELEMENT lastname (#PCDATA)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT published (#PCDATA)>
<!ATTLIST book genre (Science|Fiction) #REQUIRED>
<!ATTLIST book format (Paperback|Hardcover) "Paperback">