The xsl:choose element is analogous to the SQL searched CASE expression. This element contains one or more xsl:when elements that are analogous to WHEN clauses in SQL searched CASE expressions. A SQL searched CASE expression is one where each WHEN clause is a predicate. Like the SQL searched CASE expression, each xsl:when element takes a test attribute that contains an expression. If the expression for an xsl:when element evaluates to true, the content of that element is used. The xsl:choose element can also contain an xsl:otherwise element which is equivalent to the CASE expression's ELSE clause. If all the xsl:when elements evaluate to false, the content of the xsl:otherwise element is used. XSLT does not require that your expression be a true Boolean expression. Any expression in XSLT can evaluate to an effective Boolean value. Chapter 6 has a discussion of effective Boolean value in XQuery.