Not sure whether this is a saxon or XSLT issue (or just me for that matter).

Saxon wouldn't allow me to  set the bracketType attrtibute to "{"
(Unexpected token "<eof>" in path expression)

    <xsl:variable name="fieldNames" as="element()*">
       <this:fieldName elem="product" plural="products" bracketType="["/>
       <this:fieldName elem="productThumbnail" plural="thumbnails"
bracketType="{{"/>
    </xsl:variable

so I set it to "{{" as above, which Saxon accepts but inserts {{ into
my result tree instead of {.

I have a workaround (substring the bracketType attribute) but would
like an explanation please.