mention PCRE in docs/userguide

diff --git a/docs/userguide b/docs/userguide
index 865ee4b97f410a903786cff354c34532060ff85b..597cdb51a1a1c014f00b9ea3ee452b27aa7697b2 100644 (file)
--- a/docs/userguide
+++ b/docs/userguide
@@ -739,8 +739,9 @@ con_id::
        Compares the i3-internal container ID, which you can get via the IPC
        interface. Handy for scripting.
 
-Note that currently all criteria are compared case-insensitive and do not
-support regular expressions. This is planned to change in the future.
+The criteria +class+, +instance+, +title+ and +mark+ are actually regular
+expressions (PCRE). See +pcresyntax(3)+ or +perldoc perlre+ for information on
+how to use them.
 
 === Splitting containers