[xsl] Syntax error in regex pattern

["Scott Vanderbilt lists@xxxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Hello.

I am trying to use a regex pattern with properties in an xsl:analyze 
statement, like this:

B B B  <xsl:analyze-string select="$stringtoproc" regex="\p{L}">

with the intention of capturing letters only. However, when using this 
in an XSLT transformation in OxygenXML, I receive the following error:

Syntax error at char 2 in regular expression: Expected '{' after \112

I've googled about, looking for cases that might explain what is wrong 
with the pattern, but find very few examples in the wild that might 
point out the error.

Many thanks in advance for any assistance.

P.S. The transformation engine is Saxon-HE 9.8.0.12, running within 
OxygenXML Editor 21.1 (Windows 64), java.runtime.version 1.8.0_202-b08.