xsl:for-each order-by gives error

[Ekrem Aksoy]

When i'm trying to execute the code below cocoon gives error :error found handling the request... any comments? Thanx <xsl:for-each select="book" order-by="+ title"> <tr bgcolor="#C0C0C0"> <td><xsl:value-of select="title"/></td> <td><xsl:value-of select="author"/></td> </tr> </xsl:for-each>