Where is the source of LET* macro

Arthur Cater <[email protected]> Fri, 14 Apr 2023 21:17:41 +0100

Newsgroups	gmane.lisp.openmcl.devel
Message-ID	<[email protected]>

I can only find a define-compiler-macro, I want to see how LET* handle declarations.
It surprises me that it is apparently legal to say

 ? (let* ((it 7) (it (list it it)) (it (length it))) it)
2
? 

and I wondered how declarations (if present) are treated - but I can’t find the source code.

TIA for any hep