non-compliant restriction pattern in v3.3 nuspec.xsd

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There seems to be a non-compliant pattern in v3.3 nuspec.xsd

In reference to the fragment beginning on line 258 of v3.3 nuspec.xsd :
<xs:simpleType name="folder_type">
<xs:restriction base="xs:string">
<xs:pattern value="^vb|fs|cs/[^/]+/.+"/>
</xs:restriction>
</xs:simpleType>

XML-SPY 2019 throws the following error:
Value '^vb|fs|cs/[^/]+/.+' is not a valid XML regular expression.
Error location: xs:schema / xs:simpleType / xs:restriction / xs:pattern / @value
Details
invalid-escape: The given character escape is not recognized.
dt-pattern: Value '^vb|fs|cs/[^/]+/.+' is not a valid XML regular expression.