All callers should assure that at least this size of memory is
allocated at the place pointed by the second argument.
- Thers are 6 modifiers, each consumes 2 chars.
+ There are 6 modifiers, each consumes 2 chars.
The octal form of a character code consumes
(1 + CHARACTERBITS / 3 + 1) chars (including backslash at the head).
We need one more byte for string terminator `\0'. */