What does Joshua 16:8 mean?

From Tappuah, the border went west to the Kanah Valley and ended at the sea. This was Ephraim's land, including the towns and villages along the border that belonged to Manasseh. Joshua 16:8 - Modern Text Bible

(The western border is described, and it's noted that some towns near the border actually belonged to Manasseh, even though they were surrounded by Ephraim's land.)