perl -Mre=debug -e '"hello world" =~ /l.w/'

##</code><code>##

Freeing REx: `","'
Compiling REx `l.w'
size 6 Got 52 bytes for offset annotations.
first at 1
   1: EXACT <l>(3)
   3: REG_ANY(4)
   4: EXACT <w>(6)
   6: END(0)
anchored `l' at 0 (checking anchored) minlen 3
Offsets: [6]
        1[1] 0[0] 2[1] 3[1] 0[0] 4[0]
Guessing start of match, REx `l.w' against `hello world'...
Found anchored substr `l' at offset 2...
Starting position does not contradict /^/m...
Guessed: match at offset 2
Matching REx `l.w' against `llo world'
  Setting an EVAL scope, savestack=3
   2 <he> <llo world>     |  1:  EXACT <l>
   3 <hel> <lo world>     |  3:  REG_ANY
   4 <hell> <o world>     |  4:  EXACT <w>
                            failed...
  Setting an EVAL scope, savestack=3
   3 <hel> <lo world>     |  1:  EXACT <l>
   4 <hell> <o world>     |  3:  REG_ANY
   5 <hello> < world>     |  4:  EXACT <w>
                            failed...
  Setting an EVAL scope, savestack=3
   9 <hello wor> <ld>     |  1:  EXACT <l>
  10 <hello worl> <d>     |  3:  REG_ANY
  11 <hello world> <>     |  4:  EXACT <w>
                            failed...
Match failed
Freeing REx: `"l.w"'