How does the <class> tag work in the persistence.xml file in jpa?

Question

Good night. I’m starting in jpa studies, and in a moment I came across the following situation, I filled in the persistence.xml file as follows:

<?xml version="1.0" encoding="UTF-8"?>
    <persistence version="2.1"
        xmlns="http://xmlns.jcp.org/xml/ns/persistence"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
        <persistence-unit name="exercicios-jpa">
                <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
                <class>modelo.basico.Usuario</class>
                <class>modelo.basico.Estado</class>
                <class>modelo.basico.Cidade</class>
                <properties>
                        <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
                        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost/curso_java"/>
                        <property name="javax.persistence.jdbc.user" value="root"/>
                        <property name="javax.persistence.jdbc.password" value="12345678"/>

                        <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL57Dialect"/>
                        <property name="hibernate.show_sql" value="true"/>
                        <property name="hibernate.format_sql" value="true"/>
                        <property name="hibernate.hbm2ddl.auto" value="update"/>
                </properties>
        </persistence-unit>
    </persistence>

It worked perfectly, but on another occasion I filled in the same file only I forgot to add the tag class , and even then it worked normally, I believe this occurs because only the Annotation @Entity is enough to inform the class, I was left with doubt as to the actual use of the tag, since apparently it is not mandatory. I did research, but I only found subjective answers, and I think it serves cases where there is more than one persistence unit in the file, to identify which unit each class belongs to, but I would like the right answer so that I do not create a wrong concept. Thanks in advance.