How is filtering done in the war plugin?

Examples can be found here

How does the classifier affect artifacts in my war project?

When used, the copy of the artifact in your project will have the classifier appended to its filename. This can be used to differentiate duplicate artifacts.

How do I exclude transitive dependencies from my project?

Give it a "provided" scope.

What's the difference in using dependentWarExclude and provided scope?

dependentWarExclude is used in war overlays for excluding dependent war files from being included in the exploded war.

How do I exclude files in my web rources?

Use the webResources exclude parameter to identify the tokens to use for the filtering.

How do I exclude files when doing war overlays?

Use the dependentWarExcludes parameter to identify the tokens to use for the filtering.

For more information refer to Adding and Filtering External Web Resources

Where can I find the documentation for the plugin's configuration?

For each goal, you can use the documentation from the plugin site.

If you need a specific version, generate it using site:site or use mvn help:describe \\
-DgroupId=org.apache.maven.plugins -DartifactId=maven-war-plugin -Dfull=true \\
-Dversion>your-plugin-version-here<