Why does tomcat modify web.xml take effect without rebooting?

I always thought that in tomcat, modifying the web.xml file would not take effect until tomcat was restarted
but I tried it today. After modifying the web.xml file, the browser refreshed and the change took effect. Refresh it again and it took effect.
what"s the point? It takes effect without restarting tomcat
apache-tomcat-9.0.12

Sep.06,2021
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