> Chicken does not support the extended syntax-rules patterns added in R7RS (actually copied over from R6RS), only the more limited patterns allowed by R5RS.

If memory serves, SRFI 46 (Basic Syntax-rules Extensions) was added to
RnRS. Anything else?

Timeline:

- 1998: R5RS
- 2005: SRFI 46
- 2007: R6RS

> This is a bug in Chicken, not in my code.

The syntax-rules implementation provided by Chicken's r7rs egg seems to
be here:
https://code.call-cc.org/svn/chicken-eggs/release/5/r7rs/trunk/synrules.scm

The default syntax-rules implementation, sans r7rs, is in the
chicken-core repo in the file synrules.scm. The procedure
`segment-pattern?` raises the error "Cannot combine dotted tail and
ellipsis".