Unable to understand this xquery statement

Question

I am new to xquery and unable to understand what does it means :

$bottles=getallBottles()
$cups=getallCups()

<containers>
{
($bottles,$cups)  //this line i am unable to get
}
<containers>

Answer 1

The comma forms a sequence. Presumably $bottles is a sequence of zero-to-many items and $cups is a sequence of zero-to-many items. The comma forms a sequence of all of the items in $bottles and all of the items in $cups.

For example:

let $x := (1, 2, 3)
let $y := ('a', 'b', 'c')
return ($x,$y)

yields:

1 2 3 a b c

In the above example, the parentheses are necessary so that forming the sequence of $x, $y takes precedence over return and the entire constructed sequence is returned.

In an example similar to the original question, parentheses are unnecessary because precedence is not ambiguous:

let $x := <a><x>5</x><x>6</x></a>
let $y := <b><y>1</y><y>2</y></b>
return <container>{$x, $y}</container>

yields:

<container><a><x>5</x><x>6</x></a><b><y>1</y><y>2</y></b></container>