The servlet spec treats any jar in WEB-INF/lib as a web fragment:
"A plain old jar file in the WEB-INF/lib directory with no web-
fragment.xml is also considered a fragment" (section 8.2.1)
This change adds a web-fragment.xml giving the web fragment an
explicit name, "spring_web", and indicating there is no need
to scan for Servlet annotations in the spring-web.jar itself
through metadata-complete=true.
This allows applications that choose to include only specific
web fragments, through the <absolute-ordering> element in web.xml
to also include the "spring_web" fragment, in order to enable scanning
for WebApplicationInitializer types.
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