**<?xml version="1.0" encoding="UTF-8"?>
targetNamespace="book_shelf"
elementFormDefault="qualified">
xs:sequence
/xs:sequence
/xs:complexType
/xs:schema
倒数第二行错误提示：src-resolve.4.1: Error resolving component '书'. It was detected that '书' has no namespace, but components with no target namespace are not referenceable from schema document 'file:///F:/ day01/src/book.xsd'. If '书' is intended to have a namespace, perhaps a prefix needs to be provided. If it is intended that '书' has no namespace, then an 'import' without a "namespace" attribute should be added to 'file:///F:/day01/src/book.xsd'.
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