public static IElementType find(short idx) {
    // volatile read; array always grows, never shrinks, never overwritten
    IElementType type = ourRegistry[idx];
    if (type instanceof TombstoneElementType) {
      throw new IllegalArgumentException("Trying to access element type from unloaded plugin: " + type);
    }
    return type;
  }
public static IElementType find(short idx)