Long story short I found a commit [1] which mentioned macros. Looking at the diff suggests macros are defined using "syntax-extend" so I looked for that syntax in the current version of the code. Lo and behold [2]

[1] https://bitbucket.org/duangle/scopes/commits/ca7126d88bbd [2] https://bitbucket.org/duangle/scopes/src/1bf171c25f4047bc049...