func Expand(input string, mapping func(string) string) string
Expand replaces variable references in the input string according to the expansion spec using the given mapping function to resolve the values of variables.
func MappingFuncFor(context ...map[string]string) func(string) string
MappingFuncFor returns a mapping function for use with Expand that implements the expansion semantics defined in the expansion spec; it returns the input string wrapped in the expansion syntax if no mapping for the input is found.