In the Manifest-File of the logback-*.jar-files there are np properties like

• Implementation-Version, Implementation-Title, Implementation-Vendor
• Specification-Version, Specification-Title, Specification-Vendor

These Properties are useful to retreive Information about an package via the java.lang.Package-class.
Example:

System.out.println(
org.slf4j.Logger.class.getPackage()
.getImplementationVersion());
System.out.println(
ch.qos.logback.core.Appender.class.getPackage()
.getImplementationVersion());

First sysout returns e.g. 1.6.4, whereas second sysout returns null.