An NSAttributedString category for iOS (with a performance testing project) to convert an NSString with <sup> and <sub> HTML tags denoting superscript and subscript text into an NSAttributedString. It is up to 74.5 times faster than using NSAttributedString's initWithData:options:documentAttributes:error: initializer and can be executed on a background thread.
Suggested usage:
NSAttributedString *attributedString = [NSAttributedString JAM_AttributedStringFromString:string withMainFont:mainFont superscriptAndSubscriptFont:subscriptFont];
For more detailed info, read this Wiki.