You cannot create true multidimensional arrays, but you can create arrays in arrays. An array in an array is an element that refers to another array object. For example, if you use #set($b=[1, [4, 5], 3]) to create an array you create an array object where the second element refers to a new array object [4, 5].
An array element can also refer to an existing array object. For example, if you have created the array object [10, 20] and assigned the variable $a to it, you can use $a as element in a new array to refer to this array.
An array in an array can in turn refer to another array. For example, if you use #set($c=[1, [4, [6, 8]], 3]) to create an array you create an array object where the second element refers to a new array object [4, [6, 8]] which in turn refers to a new array object [6, 8].
