4.Not Well-formed and not valid document.
CODING:
<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE bookdb[
<!ELEMENT bookdb (author)>
<!ELEMENT author (title,fname,lname)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT fname (#PCDATA)>
<!ELEMENT lname (#PCDATA)>
]>

<!-- Neither well formed nor Valid -->
<book>
<author>
<title>Mr.</title>
<fname>Tony</fname>
<lname>Stark</lname>
  </author>