private static boolean isPossibleBuilderClass(Element possibleBuilderClass, ValueAttribute valueAttribute) {
      if (possibleBuilderClass.getKind() == ElementKind.CLASS) {
        return possibleBuilderClass.getModifiers().contains(Modifier.STATIC)
            && possibleBuilderClass.getKind() == ElementKind.CLASS
            && valueAttribute.containingType.names().possibleAttributeBuilder(possibleBuilderClass.getSimpleName());
      }

      return false;
    }
Determine if inner class could be a builder.

@param possibleBuilderClass nested value element that could be builder class.
@return true if it's a static inner class.
value-processor/src/org/immutables/value/processor/meta/AttributeBuilderReflection.java