The original poster asked:

 How to output a specific character in front of every character in a
given string?

Part I:
====
This is a problem that is easily solved with FXSL. the solution is
this one-liner:

f:str-map(f:flip(f:concat2(), '|'), string(/*))

Part II
====
Of course, it needs to be put into a stylesheet:

<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"

xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:f="http://fxsl.sf.net/"
xmlns:testmap="testmap"
exclude-result-prefixes="xs f"

 <xsl:import href="../f/func-str-dvc-map.xsl"/>
 <xsl:import href="../f/func-curry.xsl"/>
 <xsl:import href="../f/func-flip.xsl"/>

 <!-- To be applied on text.xml -->
 <xsl:output omit-xml-declaration="yes" indent="yes"/>

 <xsl:template match="/">
   <xsl:sequence select=
    "f:str-map(f:flip(f:concat2(), '|'), string(/*))"
    />
 </xsl:template>

and this woud be the place to put the </xsl:stylesheeet> end-tag when
the definition of the various f:concat2() functions were part of FXSL
(I'll be uploading them shortly).

The reasons of this splitting of what originally was one reply is that
it never came through, regardless of three attempts -- gmail somehow
desides to use bin64 encoding, which xsl-list rejects. Sorry for the
inconvenience...

--
Cheers,
Dimitre Novatchev
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Truly great madness cannot be achieved without significant intelligence.
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To invent, you need a good imagination and a pile of junk
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You've achieved success in your field when you don't know whether what
you're doing is work or play