update and re-organize the comments in compile_opts.vtc, and add a

note that I don't know at the moment how to test never_backslash_c

src/tests/compile_opts.vtc

 # -*-mode: vcl; coding: raw-text -*-
 
-# Those instructions tell emacs to use utf-8 encoding for this source;
-# you might want to set up your editor similarly.
+# Those instructions tell emacs to encode the bytes in this file as
+# is; in particular, not to use utf-8 encoding. You might want to set
+# up your editor similarly -- a number of tests will fail if the
+# encoding is changed.
 
 varnishtest "compile options"
 
-# allow_empty_class tests from pcre2 testoutput2
+# Most of the examples in this test are adapted from pcre2 testdata.
+
+# extended option is tested in compile.vtc and match.vtc
+
+# XXX
+# - tests for alt_circumflex will require backrefs
+# - tests for alt_verbnames will require retrieving the mark
+# - auto_callout not implemented yet
+# - test for dupnames will require capturing named refs
+# - how to test never_backslash_c? pcre2 testdata only mentions it in
+#   one test, and vtc can't parse the pattern, since it has more {'s
+#   than }'s.
+
+# allow_empty_class
 varnish v1 -vcl {
 	import pcre2 from "${vmod_topbuild}/src/.libs/libvmod_pcre2.so";
 	backend b { .host = "${bad_ip}"; }
@@ -293,10 +308,6 @@ varnish v1 -errvcl {vmod pcre2 error: Cannot compile '^a\u0041z' in r constructo
 	}
 }
 
-# XXX tests for alt_circumflex will require backrefs
-# XXX tests for alt_verbnames will require retrieving the mark
-# XXX auto_callout not implemented yet
-
 # caseless
 varnish v1 -vcl {
 	import pcre2 from "${vmod_topbuild}/src/.libs/libvmod_pcre2.so";
@@ -409,10 +420,6 @@ client c1 {
 	expect resp.http.r4 == "false"
 } -run
 
-# XXX test for dupnames will require capturing named refs
-
-# extended option is tested in compile.vtc and match.vtc
-
 # firstline
 varnish v1 -vcl {
 	import pcre2 from "${vmod_topbuild}/src/.libs/libvmod_pcre2.so";
@@ -468,6 +475,9 @@ client c1 {
 # systems). AFAICT the results are no different at all from the pcre2
 # standard character tables, but at least this tests against obvious
 # bugs.
+# locale_fr.vtc tests the option with "fr_FR", following pcre2
+# testdata, if autoconf can determine that the locale exists (using
+# locale -a).
 varnish v1 -vcl {
 	import pcre2 from "${vmod_topbuild}/src/.libs/libvmod_pcre2.so";
 	backend b { .host = "${bad_ip}"; }