为什么[NSURL URLWithString:]在url字符串中转义一些字符而不转义其他字符?

I found that [NSURL URLWithString:] method escapes some characters in url string passed to it automatically. e.g. it escapes brackets. But url string contains other non-legal url characters such as < and > causes the method return nilI found that [NSURL URLWithString:] method esca