When a new movement in art attains a certain fashion, it is advisable to find out what its advocates are aiming at, for, however farfetched and unreasonable their principles may seem today, it is possible that in years to come they may be regarded as normal. 

请问这句话中的 it is possible that in years to come they may be regarded as normal 这个分句中，that they may be regarded as normal 是真主语的话, in years to come 这作什么成分？