File: Data.xml
A
B
C
D
E
F
G
H
I
J
K
L
File: Transform.xslt
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
group-adjacent="(position()-1) idiv $cols">
Output:
A
B
C
D
E
F
G
H
I
J
K
L