The xsl:sequence element was new in XSLT 2.0; it is used to construct arbitrary sequences. It may select any sequence of nodes and/or atomic values, and essentially adds these to the result sequence. The input may be specified either by a select attribute, or by the instructions contained in the xsl:sequence instruction, or both (the select attribute is processed first). Nodes and atomic values are included in the result sequence directly. Unlike xsl:copy-of, no copy is made.

The most common use is to return a result from a function. For example:

<xsl:function name="f:increment" as="xs:integer"> <xsl:param name="in" as="xs:integer"/> <xsl:sequence select="$in + 1"/> </xsl:function>

There are two other interesting usage scenarios. The first is copying atomic values into a tree. For example:

<e> <xsl:sequence select="1 to 5"/> <br/> <xsl:sequence select="6 to 10"/> </e>

which produces the output <e>1 2 3 4 5<br/>6 7 8 9 10</e>.

The second, more important, is constructing a sequence-valued variable. A variable is sequence-valued if the variable binding element (e.g. xsl:variable has non-empty content, an as attribute, and no select attribute. For example:

<xsl:variable name="seq" as="xs:integer *"> <xsl:for-each select="1 to 5">> <xsl:sequence select=". * ."/> </xsl:for-each/> </xsl:variable>

This produces the sequence (1, 4, 9, 16, 25) as the value of the variable.

The xsl:sequence instruction may be used to produce any sequence of nodes and/or atomic values.

If nodes are constructed within a sequence-valued variable, they will be parentless. For example, the following code creates a variable whose value is a sequence of three parentless attributes:

<xsl:variable name="seq" as="attribute() *"> <xsl:attribute name="a">10</xsl:attribute> <xsl:attribute name="b">20</xsl:attribute> <xsl:attribute name="a">30</xsl:attribute> </xsl:variable>

It is quite legitimate to have two attributes in the sequence with the same name; there is no conflict until an attempt is made to add them both to the same element. The attributes can be added to an element by using <xsl:copy-of select="$seq"/> within an xsl:element instruction or within a literal result element. At this stage the usual rule applies: if there are duplicate attributes, the last one wins.