Adolescents, boys and girls, form deeply sentimental attachments, walk and talk together — not so much to polish their wits as to share their hopes and fears and dreams to form a common front against the world of school and family and to join in a kind of mutual discovery of each other's and their own inner life.

form a common front against the world是什么意思，对世界形成一个共同的正面（共同阵线）？