The + operator applied on sequences

The infixed operator +, with two sequences as argument, returns the total sum of the elements of the two sequences.
Note the difference with the lists, where the term by term sums of the elements of the two lists would be returned.
Input :

(1,2,3,4,5,6)+(4,3,5)

Or :

'+'((1,2,3,4,5,6),(4,3,5))

Output :

33

But input :

[1,2,3,4,5,6]+[4,3,5]

Output :

[5,5,8,4,5,6]

Warning
When the operator + is prefixed, it has to be quoted ('+').