On iOS, this should be the "PostScript name" found in Font Book after installing the font.
On Android, this should be the name of the font file (containing only lowercase alphanumeric characters) in android/app/src/main/res/font
Default
TheOS's system font
Optionalsize
size?:number
The font size for text in the element. This value is required to be greater than 0.
The font used for the element text.
On iOS, this should be the "PostScript name" found in Font Book after installing the font. On Android, this should be the name of the font file (containing only lowercase alphanumeric characters) in android/app/src/main/res/font