What are hygienic macros?

Some articles on hygienic macros, macro, hygienic macro, macros:

Scheme (programming Language) - Distinguishing Features - Implementation Standards - Hygienic Macros
... and also in later reports, the syntax of Scheme can easily be extended via the macro system ... The R5RS standard introduced a powerful hygienic macro system that allows the programmer to add new syntactic constructs to the language using a simple pattern matching ... Prior to this, the hygienic macro system had been relegated to an appendix of the R4RS standard, as a "high level" system alongside a "low level" macro system, both of which were treated as ...
Hygienic Macro
... Hygienic macros are macros whose expansion is guaranteed not to cause the accidental capture of identifiers ... capture was well known within the Lisp community prior to the introduction of hygienic macros ... Macro writers would use language features that would generate unique identifiers (e.g ...
Macro (computer Science) - Syntactic Macros - Hygienic Macros
... In the mid-eighties, a number of papers introduced the notion of hygienic macro expansion (syntax-rules), a pattern-based system where the syntactic environments of ... Hygienic macros have been standardized for Scheme in both the R5RS and R6RS standards ... The upcoming R7RS standard will also include hygienic macros ...