PATCH: [perl #58182] partial: Add /l, /u, /d regex modifiers (butinfix notation only)

Also available at git://github.com/khwilliamson/perl.git
branch remods

The attached sequence of patches adds (?dlu:...) regex modifiers, which 
we have discussed at great length on this list.  There's also a little 
comment/doc cleanup for the (?^...) patch.  Thanks to that patch, no 
tests that look at stringification need to change to accommodate these.

The (?u...) modifier is recognized by this patch, but it actually 
doesn't do anything (except turn off the other modifiers) yet.  When 
this patch, revised as necessary, is incorporated, I'll rebase and 
resubmit the patch that starts to use it.

I have a concern that something needs to be done with:
dist/B-Deparse/Deparse.pm
dump.c
ext/B/t/concise-xs.t

that I haven't done, as code was changed in those for the /r modifier 
added this summer.  However, I don't see what that should be, and my 
experiments don't show anything necessary.

• PATCH: [perl #58182] partial: Add /l, /u, /d regex modifiers (butinfix notation only) by karl williamson