Scheme has the notion of the dynamic extent of a procedure call. A number of standard Scheme procedures and syntaxes like dynamic-wind, call-with-current-continuation, and parameterize deal with the dynamic extent indirectly. The same holds true for the procedures and syntaxes dealing with continuation marks as defined by SRFI 157.

This SRFI reifies the dynamic extent into a first-class value together with a well-defined procedural interface and a syntax to create procedures that remember not only their environment at creation time but also their dynamic extent, which includes their dynamic environment.