def must_override
      %w{
        type version
        title author_name author_url provider_name provider_url
        cache_age thumbnail_url thumbnail_width thumbnail_height
      }
    end
def must_override
      %w{
        type version
        title author_name author_url provider_name provider_url
        cache_age thumbnail_url thumbnail_width thumbnail_height
      }
    end
An Array of helper methods names define_methods! must be able to override
 when is's called. In general, define_methods! tries its best _not_ to override
 existing methods, so this Array is important if some other library has
 defined a method that uses an oEmbed name. For example: Object#version