Hygienic macros

How are hygienic macro systems implemented?

"er" and "sc" are "explicitly-renaming" and "syntatic closures";
"how" means how the hygienic macro system is implemented (what is its based on); ER (explicitly-renaming macros), syntax-case, some native implementation in C or Java etc.
"where" is the source location of the basic hygienic syntax code.

system	syntax-rules	syntax-case	er	sc	how	where
Chez	Y	Y			syntax-case
Chibi	Y	Y	Y		ER over SC	`lib/init7.scm`
Chicken	Y	N	Y		ER	`synrules.scm expand.scm`
Gauche	Y	N !	Y		syntax-rules written in C	`src/macro.c`
Guile	Y	Y	N		syntax-case	`module/ice-9/safe-r5rs.scm module/ice-9/psyntax.scm`
Kawa	Y	Y			syntax-rules written in Java	`kawa/lang/Syntax{Pattern,Rule,Rules}.java kawa/standard/syntax_case.java kawa/lang/SyntaxForms.java`
LIPS	Y	N	N	N	syntax-rules written in Javascript	`lips.js`
Loko	Y	Y			syntax-case	`psyntax`
MIT	Y	N	Y	Y	ER	`src/runtime/syntax-rules.scm`
Peroxide	Y	N !	Y	Y	ER over SC	`src/primitives/syntactic_closure.rs` `src/scheme-lib/init.scm`
Sagittarius	Y	Y	Y		syntax-case; ER separate	`boot/lib/macro.scm`
STklos	Y	N	N	N	define-macro (no lexical scope)	`lib/mbe.stk`
Unsyntax	Y	Y			syntax-case	`src/unsyntax/expander/syntax-case.scm src/unsyntax/syntax.scm`
Ypsilon	Y	Y	N	N	syntax-rules in Scheme; portable syntax-case	`heap/boot/macro/expand.scm`, `stdlib/core/syntax-case.scm`

! = at least seems to be planned