I'm confused:

~/Downloads/chibi-scheme/lib:master$ grep -R '(define (string-cursor->index' *
chibi/string-test.sld:      (define (string-cursor->index str i) i))))
chibi/string.sld:      (define (string-cursor->index str i) i)
chibi/regexp.sld:      (define (string-cursor->index str off) off)
init-7.scm:  (define (string-cursor->index str off) off)