I read it somewhere, but I can't recall it now.

I'll also implement it this way if I was Larry:)

I find it odd that Larry you would waste memory like that.

See dave_the_m's post. He explains how even the ungreyed box is in previously allocated memory.

You mentioned it's in previously allocated memory

why??Isn't it created on the fly?

Perl allocates more memory than required for string, that's what xpv_cur/xpv_len is there for