Using a backslash "escapes" the following character.

That's not entirely true in this case: if the first character following a backslash is a digit [0-7], the sequence of up to 3 octal digits following is the escape sequence, and the resulting octal number is converted to the character with that index:

  perl -wle '$s = "\100"; print ord($s)'
  64
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Similarly, "\x" introduces a sequence of up to 2 hex digits, eg "\x3f". In Unicode-aware perls (perl-5.6.0 and later) you can also introduce codepoints above 255 by putting braces around the hex number:

  perl -wle '$s = "\x{1000}"; print ord($s)'
  4096
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Hugo