XSL : How to pass variable to for each - xslt-1.0

Question

<xsl:for-each select="$script/startWith">
<xsl:variable name = "i" >
<xsl:value-of select="$script/startWith[position()]"/>
</xsl:variable>
<xsl:for-each select="JeuxDeMots/Element">
<xsl:variable name = "A" >
<xsl:value-of select="eName"/>
</xsl:variable>
<xsl:if test="starts-with($A,$i)= true()">
<xsl:variable name="stringReplace">
<xsl:value-of select="substring($i,0,3)"/>
</xsl:variable>
<xsl:value-of select="$stringReplace"/>
</xsl:if>
</xsl:for-each>
</xsl:for-each>
Problem : variable $i, can not pass in an xsl for-each.
Please help me.

Answer 1

Try replacing the declaration of i with
<xsl:variable name="i" select="string(.)"/>
The context item (i.e. ".") is different for each evaluation of the for-each instruction, but the value of the expression $script/startWith[position()] does not change. (Here, you are making a sequence of startWith elements, and testing each one for the effective boolean value of the expression position(). The expression position() returns a positive integer, so its effective boolean value is always true. So the predicate [position()] is doing no work at all here.
Also, you'll want to replace the declaration of stringReplace with
<xsl:variable name="stringReplace" select="substring($i,1,3)"/>
(String offsets begin with 1 in XPath, not with 0.)
I am guessing that you want to process all of the startWith children of $script, and for each one emit the first three characters of the startWith value once, for each startWith/JeuxDeMots/Element whose eName child begins with the value of startWith.
Actually, the whole thing might be a little easier to read if it were briefer and more direct:
<xsl:for-each select="$script/startWith">
<xsl:variable name = "i" select="string()"/>
<xsl:for-each select="JeuxDeMots/Element">
<xsl:if test="starts-with(eName,$i)">
<xsl:value-of select="substring($i,1,3)"/>
</xsl:if>
</xsl:for-each>
</xsl:for-each>
It makes perfect sense to create the variables $A and $stringReplace if they are used several times in code you're not showing us, but if not, ...

Answer 2

I think the problem is that you change context in first for-each. Then the element JeuxDeMots is not "visible" for second for-each. You can for example try to store it in variable and use this variable in second for-each (there are also another ways how to figure out this problem).
<xsl:template match="/">
<xsl:variable name="doc" select="JeuxDeMots"/>
<xsl:choose>
<xsl:when test="$script/startWith">
<xsl:for-each select="$script/startWith">
<xsl:variable name="i">
<xsl:value-of select="."/>
</xsl:variable>
<xsl:for-each select="$doc/Element">
<xsl:variable name="A">
<xsl:value-of select="eName"/>
</xsl:variable>
<xsl:if test="starts-with($A,$i) = true()">
<xsl:variable name="stringReplace">
<xsl:value-of select="substring($i,0,3)"/>
</xsl:variable>
<xsl:value-of select="$stringReplace"/>
</xsl:if>
</xsl:for-each>
</xsl:for-each>
</xsl:when>
</xsl:choose>
</xsl:template>
Although I'm not sure what exactly you are dealing with it seems to output desired value AsAt.
You could also consider C.M.Sperberg-McQueen post about string offset in XPath.