Creates a new Case for instances of type Value, specifying the context in which that type may be substituted, and after context.

For example, the case defined by,

Case(Param, AfterParam) { (p: Int) => s"'$p'" }

handles substitutions at a hole with a hypothetical Param Context of integer values, converting them to a string by wrapping them in single-quotes, and specifying the hypothetical AfterParam Context for the continuation of parsing, following the substitution.

For any Interpolator which parses the interpolated string, allows substitutions, and uses multiple Contexts, the after value is important in determining how making the substitution changes the parse context. For example, considering the hole in,

json"""{ "key": $value }"""

prior to the substitution of value, the Context would be a value representing a position where any JSON value may be substituted, but following the substitution, i.e. after the JSON value has been substituted, the parsing context has changed, as we would only permit a comma (followed by more key/value pairs), or a closing brace; nothing else is acceptable. We would therefore specify an after Context which represents this state.