使用jquery 1.7 及以后的版本 attr 问题

if ( notxml ) {
            name = name.toLowerCase();
            hooks = jQuery.attrHooks[ name ] || ( rboolean.test( name ) ? boolHook : nodeHook );
        }

attr: function( elem, name, value, pass ) {
        var ret, hooks, notxml,
            nType = elem.nodeType;

        // don‘t get/set attributes on text, comment and attribute nodes
        if ( !elem || nType === 3 || nType === 8 || nType === 2 ) {
            return;
        }

        if ( pass && jQuery.isFunction( jQuery.fn[ name ] ) ) {
            return jQuery( elem )[ name ]( value );
        }

        // Fallback to prop when attributes are not supported
        if ( typeof elem.getAttribute === "undefined" ) {
            return jQuery.prop( elem, name, value );
        }

        notxml = nType !== 1 || !jQuery.isXMLDoc( elem );

        // All attributes are lowercase
        // Grab necessary hook if one is defined
        if ( notxml ) {
            name = name.toLowerCase();
            hooks = jQuery.attrHooks[ name ] || ( rboolean.test( name ) ? boolHook : nodeHook );
        }

        if ( value !== undefined ) {

            if ( value === null ) {
                jQuery.removeAttr( elem, name );
                return;

            } else if ( hooks && "set" in hooks && notxml && (ret = hooks.set( elem, value, name )) !== undefined ) {
                return ret;

            } else {
                elem.setAttribute( name, "" + value );
                return value;
            }

        } else if ( hooks && "get" in hooks && notxml && (ret = hooks.get( elem, name )) !== null ) {
            return ret;

        } else {

            ret = elem.getAttribute( name );//此处取属性的方法对属性名称是大小写敏感的

            // Non-existent attributes return null, we normalize to undefined
            return ret === null ?
                undefined :
                ret;
        }