Materialdesigninxamltoolkit: Prefix for TextBox

[yanxiaodi]

Thanks all contributors of this awesome project and I am wondering if we can have a prefix for the TextBox? Just like the suffix like this:

I didn't find any attributes that meet my requirement. Thank you very much.

[jespersh]

It is in the spec today it seems: https://material.io/components/text-fields search for "prefix".

Example with $:

Just hacking in a $ example:

[mgnslndh]

Should this issue be considered as fixed or is there any work left to do?