Android resource for a specific product

i got this code from Settings app...

<string name="about_settings" product="tablet">About tablet</string>
<string name="about_settings" product="default">About phone</string>

then my questions are:

1. from where at runtime the system load the correct string resource ?

2. What must I do to add a new product? e.g.

   <string name="about_settings" product="laptop">About laptop</string>