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Sequence Flow Control and Typing

XPath sequences are flat, ordered lists of items (nested sequences are automatically flattened). Flow-control constructs (for, let, if/then/else, some/every ... satisfies) and typing operators (instance of, castable as, cast as, treat as) build on this sequence model. See also FLWOR for the equivalent, more general expressions available in XQuery.

Each of the following expressions evaluates to the same sequence, (1, 2, 3, 4, 5, 6):
(3 idiv 2, (2, (3)), (), 4 to 6)
reverse(reverse(1 to 6))
(1 to 6)[. mod 1 eq 0]
(1 to 6)[. < 10]
(0 to 5)!(. + 1)
(1 to 3)!(.*2-1 , .*2)
let $a := (1 to 3), $b := (4 to 6) return ($a, $b)
for $i in (0,3), $j in (1,2,3) return ($i + $j)
if (5 le 5) then (1 to 6) else (0)
(1 to 6) treat as xs:decimal+

Each of the following expressions evaluates to true:
2 = (1,2,3)
3 > (2,4)
(1,2) = (2,3)
(1,2) != (2,3)
some $x in (1 to 3), $y in (2 to 4) satisfies $x + $y < 4
every $x in (1 to 3), $y in (2 to 4) satisfies $x + $y > 0
15 instance of xs:integer
15 instance of item()
(1,2) instance of xs:integer+
xs:unsignedByte(1) instance of xs:integer
xs:dateTime('2015-03-04T12:00:00') instance of xs:anyType
xs:dayTimeDuration('P9DT15H30M30S') instance of xs:duration
1.3 castable as xs:integer
1.3 cast as xs:boolean
xs:date('2015-08-31') > xs:date('2015-07-31')

A general comparison such as (1,2) = (2,3) is true if any pairing of items from the two sequences satisfies the comparison — it is equivalent to 1=2 or 1=3 or 2=2 or 2=3.


Each of the following expressions evaluates to the duration P30D (30 days):
xs:dayTimeDuration("P30D")
"P30D" cast as xs:dayTimeDuration?
xs:dayTimeDuration('P20D') + xs:dayTimeDuration('P10D')
xs:date('2015-03-04') - xs:date('2015-02-02')

ch03-sequence-flow.xpath.txt:
for $i in (0,3), $j in (1,2,3) return ($i + $j)

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