Problem with validation of XSD 1.1

Hello,

at first: sorry for every grammar and typing error in the following lines, but english isn't my native language ..... I hope that it's readable yet :).

Actually I try to validate a xml schema v1.1 (because I want to use the assert functionality) with PhpStorm 7.0, but the validation of the xsd file fails and I get the following error message:

cvc-complex-type.2.4.a: Invalid content was found starting with element 'xs:assert'. One of '{"http://www.w3.org/2001/XMLSchema":attribute, "http://www.w3.org/2001/XMLSchema":attributeGroup, "http://www.w3.org/2001/XMLSchema":anyAttribute}' is expected.

I was not really sure about if this is a problem of the IDE, or if I did something wrong with the XSD ... so I searched for a solution of this problem, but haven't found something yet.

I would be glad, if someone can give me an advice on how this could be done.

By the way - this is the example xsd file I tried:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
        xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="http://tf/test" targetNamespace="http://tf/test"
        elementFormDefault="qualified">

    <xs:element name="root" type="rootType"/>

    <xs:complexType name="rootType">
        <xs:all minOccurs="0">

            <xs:element name="example">
                <xs:complexType>
                    <xs:sequence>
                        <xs:element name="example_1"/>
                        <xs:element name="example_2"/>
                        <xs:element name="example_3" minOccurs="0"/>
                        <xs:element name="example_4"/>
                    </xs:sequence>
                    <xs:assert test="(example_4 = '1' and not(example_3))"/>
                </xs:complexType>
            </xs:element>

        </xs:all>
    </xs:complexType>
</xs:schema>

Regards.