With XML Schema 1.1, I sometimes prefer <xs:assertion test="matches(..)"/> over <xs:pattern value=".."/>, particularly for complex regexes. With XPath 2.0 fn:matches, we can use regex flags as defined by XPath 2.0 F&O spec (https://www.w3.org/TR/xquery-operators/#regex-syntax), to break long regex into multiple lines for readability. For e.g, translating above cited XSD simpleType would look like following (not tested) with  xs:assertion,

<xs:simpleType name="Test2">
        <xs:restriction base="xs:string">
            <xs:assertion test="matches($value, 'A

                                                                        | B

                                                                        | \?', 'mx')" />
        </xs:restriction>
</xs:simpleType>

(this can be even more helpful, when regexes are much more complex)