Use the source, Luke. 
regex prefix_circumfix_meta_operator:reduce (--> List_prefix) {
    $<s> = (
        '['
        [
        | <op=infix> ']' ['«'|<?>]
        | <op=infix_prefix_meta_operator> ']' ['«'|<?>]
        | <op=infix_circumfix_meta_operator> ']' ['«'|<?>]
        | \\<op=infix> ']' ['«'|<?>]
        | \\<op=infix_prefix_meta_operator> ']' ['«'|<?>]
        | \\<op=infix_circumfix_meta_operator> ']' ['«'|<?>]
        ]
    ) <?before \s | '(' >
...

[download]

So [\ is really a handled specially.

Or if you're not inclined to read the source, you can examine the match tree: 

$ cat test.t 
[\~] 1..3
$ perl5.10.0 STD5_dump_match test.t 
comp_unit:
 statementlist:
  statement:
   EXPR:
    left:
     pre:
      prefix_circumfix_meta_operator:
       [\
       op:
        ~
       ]
       
     noun:
      value:
       number:
        integer:
         1
    infix:
     ..
    right:
     noun:
      value:
       number:
        integer:
         3
     \n

[download]
The output in a terminal is coloured, and much better readable. Basically you see that [\ is matched as a prefix_circumfix_meta_operator with the op: ~

In reply to Re^4: Generate the perl sequence 1, 11, 111, .... by moritz
in thread Generate the perl sequence 1, 11, 111, .... by alih110

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