constructor(token) {
    this.name = token.key;
    this.field = token.field || {};
    this.value = clean(token.initial || this.field.initial || '');
    this.message = token.message || this.name;
    this.cursor = 0;
    this.input = '';
    this.lines = [];
  }
This file contains the interpolation and rendering logic for
the Snippet prompt.