We definitely seem to be at odds with /m and /s. ... I rarely need those: sometimes I need one of them; I need both far less often.

My motive for always using the  /ms modifier cluster (in addition to /x, of course) is to foster clarity, and clarity is always a necessity :) Clarity is improved because the  . ^ $ operators have unvarying behaviors. Sometimes one is forced to be devious and must sacrifice clarity of expression, but that's what comments are for!

... the qr{(?mods:...)} form over the qr{...}mods form ... The latter form makes the modifiers global: you can't get finer control such as qr{(?mo:...)(?ds:...)} or qr{(?mo:...(?ds:...)...)}.

The docs say this finer control is possible:  (?mo-ds) and  (?mo-ds:pattern) are rigorously scoped:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = qq{aa \n bb \n cc};
 ;;
 print qq{A: match, \$1 '$1' @ $-[1]  \$2 '$2' @ $-[2]  \$3 '$3' @ $-[
+3]}
   if $s =~ m{
     \A ((?-s: .+)) .+ ((?-s: .+)) .+ ((?-s: .+)) \z
     }xms;
 ;;
 print qq{B: match, \$1 '$1' @ $-[1]}
   if $s =~ m{
     \A ((?-s: .+)) \z
     }xms;
 ;;
 print qq{C: match, \$1 '$1' @ $-[1]}
   if $s =~ m{
     \A ((?-s: (?s: .+))) \z
     }xms;
"
A: match, $1 'aa ' @ 0  $2 ' ' @ 9  $3 'c' @ 11
C: match, $1 'aa
 bb
 cc' @ 0
[download]

(Tricky to put together a meaningful example for this!)

That said, I would never write regex A as above, but rather as:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = qq{aa \n bb \n cc};
 ;;
 print qq{A: match, \$1 '$1' @ $-[1]  \$2 '$2' @ $-[2]  \$3 '$3' @ $-[
+3]}
   if $s =~ m{
     \A ([^\n]+) .+ ([^\n]+) .+ ([^\n]+) \z
     }xms;
"
A: match, $1 'aa ' @ 0  $2 ' ' @ 9  $3 'c' @ 11
[download]

Don't mess with dot (or  ^ $ either): much less potential for brain-hurt.

Update: Another version of regex A:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = qq{aa \n bb \n cc};
 ;;
 print qq{A: match, \$1 '$1' @ $-[1]  \$2 '$2' @ $-[2]  \$3 '$3' @ $-[
+3]}
   if $s =~ m{
     \A (?-s) (.+) (?s) .+ (?-s) (.+) (?s) .+ (?-s) (.+) \z
     }xms;
"
A: match, $1 'aa ' @ 0  $2 ' ' @ 9  $3 'c' @ 11
[download]

In the context of global dot-matches-newline behavior, successive  (?-s) and  (?s) turn newline matching off and on, respectively. Again, I wouldn't actually write a regex this way unless my feet were being held to the fire.

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