,y gives a list of the atoms of y in “normal” order: 
the result is ordered by items, by items within items, etc.  
The result shape is 1$*/$ y . Thus: 
   y=: 2 4 $ 'abcdefgh'
   y
abcd
efgh
   ,y
abcdefgh
 
 | 
  | 
x,y appends items of y to items of x after: 
 
| 1. | 
Reshaping an atomic argument to the 
shape of the items of the other,  |  
  
| 2. | 
Bringing the arguments to a common rank 
(of at least 1) by repeatedly 
itemizing (,:) 
any of lower rank, and |  
  
| 3. | 
Bringing them to a common shape by padding with fill 
elements in the manner described in 
Section II B.  |  
 
 
The fit conjunction (,!.f) provides fill 
specified by the atom f .
   |