Complex sentence: Chapters are classified as Meccan or Medinan, depending on whether the verses were revealed before or after the migration of Muhammad to the city of Medina, however, a chapter classified as Medinan may contain Meccan verses in it and vice versa.
Split into simpler sentences: Chapters are classified as Meccan or Medinan, depending on whether the verses were revealed before or after the migration of Muhammad to the city of Medina. However, a chapter classified as Medinan may contain Meccan verses in it and vice versa.