use YAPE::Regex::Explain;
say YAPE::Regex::Explain->new( qr{/(\d.*?)/i} )->explain;

##</code><code>##

----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \d                       digits (0-9)
----------------------------------------------------------------------
    .*?                      any character except \n (0 or more times
                             (matching the least amount possible))
----------------------------------------------------------------------
  )                        end of \1

##</code><code>##

----------------------------------------
        \d       one digit <br>
----------------------------------------
        .*?      anything (except a newline), with as few as 
                     zero instances (times) of anything
                     ...and absolutely no more than (in the case of your 
                     sample data) 'one additional digit'."
----------------------------------------