String library, see the documentation for SRFI-1318
The file srfi-13-syntax.scm contains macro definitions for let-string-start+end.
On systems that support dynamic loading, the srfi-13 unit can be made available in the interpreter (csi) by entering
(require 'srfi-13)
18 http://srfi.schemers.org/srfi-13/srfi-13.html