Joining/merging several cell arrays

The standard concatenation brackets work with cell arrays just as with numerical arrays:

 >> cell1 = {'a' 'b' 'c'};
 >> cell2 = {'d' 'e' 'f'};
 >> cell3 = [cell1 cell2]

 cell3 = 

    'a'    'b'    'c'    'd'    'e'    'f'

 >> cell4 = [cell1; cell2]

 cell4 = 

    'a'    'b'    'c'
    'd'    'e'    'f'

But I don't know what "using some key vectors" means, so maybe it's more complex than this.

Thank you both.