Difference between ${scmBranch} and $\{scmBranch} for maven-jar-plugin/ maven-war-plugin

Question

I do use the maven-jar-plugin in my pom.xml.

<plugin>
   <artifactId>maven-jar-plugin</artifactId>
   <configuration>
      <archive>
         <manifestEntries>
            <SCM-Revision>${buildNumber}</SCM-Revision>
            <SCM-Branch>${scmBranch}</SCM-Branch>
         </manifestEntries>
      </archive>
   </configuration>
</plugin>

Opening it with IntelliJ ${scmBranch} I do get following message: "cannot resolve symbol 'scmBranch' .."

Property ${buildNumber} seems to be ok - no complaining here.

If I change ${scmBranch} to $\{scmBranch} as in the documentation error dissapear.

What is exactly the difference between stating a maven property as ${} and $\{}?