iOS7 and later, we can use - (void)drawWithRect:(CGRect)rect options:(NSStringDrawingOptions)options attributes:(NSDictionary *)attributes context:(NSStringDrawingContext *)context to calculate the string size, but I'm confused with the comments on NSStringDrawingOptions enum.
NSStringDrawingUsesLineFragmentOrigin
It means specified origin is the line fragment origin, not the base line origin. But what mean of line fragment origin and baseline origin.
Just like the WWDC 2013 Session 220 (Advanced Text Layouts and Effects with Text Kit) PDF on Page 95.
If line fragment origin mean the blue dot, what the baseline origin?
From the official documentation
Discussion
If NSStringDrawingUsesLineFragmentOrigin is specified in options, it wraps the string text as needed to make it fit. If the string is too big to fit completely inside the rectangle, the method scales the font or adjusts the letter spacing to make the string fit within the given bounds.
If NSStringDrawingUsesLineFragmentOrigin is not specified in options, the origin of the rectangle is the baseline of the only line. The text will be displayed above the rectangle and not inside of it. For example, if you specify a rectangle starting at 0,0 and draw the string ‘juxtaposed’, only the descenders of the ‘j’ and ‘p’ will be seen. The rest of the text will be on the top edge of the rectangle.
This method draws the line using the attributes specified in the attributed string itself. If newline characters are present in the string, those characters are honored and cause subsequent text to be placed on the next line underneath the starting point.
Special Considerations This method uses the baseline origin by default, so it renders the string as a single line. To render the string in multiple lines, specify NSStringDrawingUsesLineFragmentOrigin in options.
来源：https://stackoverflow.com/questions/28362844/confused-by-nsstringdrawingoptions-item-meaning