code: function(value) {
      if (!this.context) return;
      if (this.setter === false) return;
      if (!this.setter) {
        try {
          this.setter = typeof this.expression === 'string'
            ? expressions.parseSetter(this.expression, this.observations.globals, this.observations.formatters)
            : false;
        } catch (e) {
          this.setter = false;
        }
        if (!this.setter) return;
      }
  
      try {
        var result = this.setter.call(this.context, value);
      } catch(e) {
        return;
      }
  
      // We can't expect code in fragments outside Observer to be aware of "sync" since observer can be replaced by other
      // types (e.g. one without a `sync()` method, such as one that uses `Object.observe`) in other systems.
      this.sync();
      this.observations.sync();
      return result;
    }
docs: Sets the value of this expression