HostRegexp() fails with a regexp, works with literal

Traefik 3.0.4: When I use this in a router:

rule: HostRegexp(\.+)

I get no routing (404 from router). Everything works fine when I put what should be a literal there instead of regex:

rule: HostRegexp(d10.ddev.site)

This is all with simple file provider, and a super-simplified working router and service, all of which work until I use a regex.

Simple things (should be simple) like

HostRegexp(d10\.ddev\.site)
also fail, and adding anchors to front and end (as in docs examples) also fails with 404.

What am I missing here? Thanks for the help and the great project.

(I wasn't able to figure out how to put the backticks into this editor, but they're there, so each example above has HostRegexp(backtick-regex-backtick) )

The problem was that I was using defaultRuleSyntax: v2 in the static configuration.

I added ruleSyntax: v3 to the rule and all of this works correctly. I didn't realize there was so much difference in v2/v3 HostRegexp()