Where do these values come from? The documentation for android:fontFamily does not list this information in any place
These are indeed not listed in the documentation. But they are mentioned here under the section 'Font families'. The document lists every new public API for Android Jelly Bean 4.1.
In the styles.xml file in the application I'm working on somebody listed this as the font family, and I'm pretty sure it's wrong:
Yes, that's wrong. You don't reference the font file, you have to use the font name mentioned in the linked document above. In this case it should have been this:
<item name="android:fontFamily">sans-serif</item>
Like the linked answer already stated, 12 variants are possible:
Added in Android Jelly Bean (4.1) - API 16 :
Regular (default):
<item name="android:fontFamily">sans-serif</item>
<item name="android:textStyle">normal</item>
Italic:
<item name="android:fontFamily">sans-serif</item>
<item name="android:textStyle">italic</item>
Bold:
<item name="android:fontFamily">sans-serif</item>
<item name="android:textStyle">bold</item>
Bold-italic:
<item name="android:fontFamily">sans-serif</item>
<item name="android:textStyle">bold|italic</item>
Light:
<item name="android:fontFamily">sans-serif-light</item>
<item name="android:textStyle">normal</item>
Light-italic:
<item name="android:fontFamily">sans-serif-light</item>
<item name="android:textStyle">italic</item>
Thin :
<item name="android:fontFamily">sans-serif-thin</item>
<item name="android:textStyle">normal</item>
Thin-italic :
<item name="android:fontFamily">sans-serif-thin</item>
<item name="android:textStyle">italic</item>
Condensed regular:
<item name="android:fontFamily">sans-serif-condensed</item>
<item name="android:textStyle">normal</item>
Condensed italic:
<item name="android:fontFamily">sans-serif-condensed</item>
<item name="android:textStyle">italic</item>
Condensed bold:
<item name="android:fontFamily">sans-serif-condensed</item>
<item name="android:textStyle">bold</item>
Condensed bold-italic:
<item name="android:fontFamily">sans-serif-condensed</item>
<item name="android:textStyle">bold|italic</item>
Added in Android Lollipop (v5.0) - API 21 :
Medium:
<item name="android:fontFamily">sans-serif-medium</item>
<item name="android:textStyle">normal</item>
Medium-italic:
<item name="android:fontFamily">sans-serif-medium</item>
<item name="android:textStyle">italic</item>
Black:
<item name="android:fontFamily">sans-serif-black</item>
<item name="android:textStyle">italic</item>
For quick reference, this is how they all look like:
