XSLT xsl:sequence. What is it good for..?

Question

I know the following question is a little bit of beginners but I need your help to understand a basic concept.

I would like to say first that I\'m a XSLT programmer

Answer 1

on an atomic value (or sequence of atomic values) is the same as both just return a copy of their input. The difference comes when you consider nodes.

If $n is a single element node, eg as defined by something like

Then

Returns a copy of the node, it has the same name and child structure but it is a new node with a new identity (and no parent).

Returns the node $n, The node returned has the same parent as $n and is equal to it by the is Xpath operator.

The difference is almost entirely masked in traditional (XSLT 1 style) template usage as you never get access to the result of either operation the result of the constructor is implicitly copied to the output tree so the fact that xsl:sequence doesn't make a copy is masked.

is the same as

Both make a new element node and copy the result of the content as children of the new node x.

However the difference is quickly seen if you use functions.

    
        hello
    

    
        ::
        :: 
        :: 
        ::
        :: 
        :: 
        ::
    

    
        
        
    

    
        
        
    

Produces

$ saxon9 -it main seq.xsl

::
:: true
:: false
::
:: 1
:: 0
::

Here the results of xsl:sequence and xsl:copy-of are radically different.