Which element in this XML code is not a good candidate for conversion into an attribute?

1 <superheroes>
2 <name>Superman</name>
3 <alias>Clark Kent</alias>
4 <birthplace>Krypton</birthplace>
5 <power>Flight</power>
6 <power>X-Ray Vision</power>
7 <power>Super Strength</power>
8 </superheroes>