Typing variables

If I have an element <elem>A,B,C</elem> and I want it to render as
JSON - "elem":["A","B","C"], so I do

"<xsl;value-of select="local-name(),$thinge" separator='":['/>] where $thing is

<xsl:variable name="thing">"<xsl:value-of
select="replace(.,',',concat($quot,',',$quot))"/>"</xsl:variable> and
the value of the variable $quot is obvious.

If I were to make $thing a typed variable what would it  be.