注册meta格式 Failed to register meta to .abc, the metaCtor is not extended from RawAssetMeta

[ctxdecoco (badboy)]

使用Editor.assetdb.remote.register(".abc", false, ABCMeta)
提示
Failed to register meta to .abc, the metaCtor is not extended from RawAssetMeta

这个RawAssetMeta怎么获取