code: private MethodSpec.Builder buildSkeletonType(Set<String> dateSkeletons, Set<String> timeSkeletons) {
      MethodSpec.Builder method = MethodSpec.methodBuilder("skeletonType")
          .addJavadoc("Indicates whether a given skeleton pattern is a DATE or TIME.\n")
          .addModifiers(PUBLIC, STATIC)
          .addParameter(String.class, "skeleton")
          .returns(SKELETON);
  
      method.beginControlFlow("switch (skeleton)");
      
      for (String skel : dateSkeletons) {
        method.addCode("case $S:\n", skel);
      }
      method.addStatement("  return $T.DATE", SKELETON);
      
      for (String skel : timeSkeletons) {
        method.addCode("case $S:\n", skel);
      }
      method.addStatement("  return $T.TIME", SKELETON);
  
      method.addCode("default:\n");
      method.addStatement("  return null");
      method.endControlFlow();
  
      return method;
    }
docs: Constructs a method to indicate if the skeleton is a DATE or TIME, or null if unsupported.