code: function (attr, value, keepKey) {
              // Convert `attr` to attr parts (if it isn't already).
              var parts = attrParts(attr, keepKey),
                  // The immediate prop we are setting.
                  prop = parts.shift(),
                  // The current value.
                  current = this.__get(prop);
  
              // If we have an `object` and remaining parts.
              if (canMakeObserve(current) && parts.length) {
                  // That `object` should set it (this might need to call attr).
                  current._set(parts, value)
              } else if (!parts.length) {
                  // We're in "real" set territory.
                  if (this.__convert) {
                      value = this.__convert(prop, value)
                  }
                  this.__set(prop, value, current)
              } else {
                  throw "can.Observe: Object does not exist"
              }
          }
docs: Sets `attr` prop as value on this object where. `attr` - Is a string of properties or an array  of property values. `value` - The raw value to set.