MatButtonToggleGroupMultiple lacks value property and change event #9058
Description
Feature request:
The docs clearly indicate that when using the MatButtonToggleGroup with the multiple directive, that you can no longer access the values of the control. While that is very informative, it makes the multiple variant of this control almost entirely unusable in a form. Without a change event or a value, you have to hack in things like click events just to get the selected values.
What is the expected behavior?
The MatButtonToggleGroupMultiple class should ideally inherit all of the functionality currently in the MatButtonToggleGroup class
What is the current behavior?
Currently, it inherits practically none of it.
What is the use-case or motivation for changing an existing behavior?
Without being able to easily access the selected values, how are we supposed to use these in our forms?
Which versions of Angular, Material, OS, TypeScript, browsers are affected?
Material 5.0.1