[xsl] [XSL 3.0] Function that check if a xs:string can be converted as a xs:double

["Christophe Marchand cmarchand@xxxxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Hello !

I have to write a function taht take a xs:string as parameter, returns a 
xs:boolean, and says true() if string is a valid number, false() otherwise.

Something like

|<xsl:function name="f:isNumber" as="xs:boolean"> <xsl:param 
name="expression" as="xs:string"/> <xsl:sequence select="....."/> 
</xsl:function> |

|'1' -> true() '2' -> true() 'foo' -> false() 'bar' -> false() |

Rules to be a valid number are the same as those used in number() function.

Any help wil be much appreciated !

Christophe

b