docs: public final String getImplementationVersion()
      {
          if (implementationVersion == null) {
              Enumeration<URL> urls;
              try {
                  urls = Context.class.getClassLoader().getResources("META-INF/MANIFEST.MF");
              } catch (IOException ioe) {
                  return null;
              }
  
              // There will be many manifests in the world -- enumerate all of them until we find the right one.
              while (urls.hasMoreElements()) {
                  URL metaUrl = urls.nextElement();
                  InputStream is = null;
                  try {
                      is = metaUrl.openStream();
                      Manifest mf = new Manifest(is);
                      Attributes attrs = mf.getMainAttributes();
                      if ("Mozilla Rhino".equals(attrs.getValue("Implementation-Title"))) {
                          implementationVersion =
                              "Rhino " + attrs.getValue("Implementation-Version") + " " + attrs.getValue("Built-Date").replaceAll("-", " ");
                          return implementationVersion;
                      }
                  } catch (IOException e) {
                      // Ignore this unlikely event
                  } finally {
                      try {
                          if (is != null) is.close();
                      } catch (IOException e) {
                          // Ignore this even unlikelier event
                      }
                  }
              }
          }
  
          return implementationVersion;
      }