AttributeSet 的意义

    /**
     * Return an AttributeSet interface for use with the given XmlPullParser.
     * If the given parser itself implements AttributeSet, that implementation
     * is simply returned.  Otherwise a wrapper class is
     * instantiated on top of the XmlPullParser, as a proxy for retrieving its
     * attributes, and returned to you.
     *
     * @param parser The existing parser for which you would like an
     *               AttributeSet.
     *
     * @return An AttributeSet you can use to retrieve the
     *         attribute values at each of the tags as the parser moves
     *         through its XML document.
     *        
     * @see AttributeSet
     */
    public static AttributeSet asAttributeSet(XmlPullParser parser) {
        return (parser instanceof AttributeSet)
                ? (AttributeSet) parser
                : new XmlPullAttributes(parser);
    }

在google android源码 Xml.java 文件中