[xsl] case conversion with replace() (i.e., with a regular expression)

["Wolfhart Totschnig wolfhart.totschnig@xxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Dear list,

I need to convert the first character of a string from lower-case to 
upper-case. I know that I can do so with the following code:

concat(upper-case(substring(.,1,1)),substring(.,2))

I was wondering whether it can also be done with the replace() function, 
i.e., with a regular expression. I found out that some regular 
expression versions have the command \u for that. So I tried the following:

replace(.,'^(.)','\u$1')

But this produces an error with Saxon ("FORX0004: Invalid replacement 
string in replace(): \ character must be followed by \ or $"). Does this 
mean that case conversion is not available in the regular expression 
version implemented in XSLT? Or did I get the code wrong?

Thanks in advance for your help!
Wolfhart