This directory contains definitions for all the SassScript value types. These definitions are used both to represent SassScript values internally and in the public Dart API. They are usually produced by the evaluator as it evaluates the expression-level Sass AST.
Sass values are always immutable, even internally. Any changes to them must be done by creating a new value. In some cases, it's easiest to make a mutable copy, edit it, and then create a new immutable value from the result.