XPaths are like file system paths. If the last component of a path is a directory, it's a directory path. If the last component of a path is a file, it's a file path.

In your case, the last component ("test") is an attribute, so you're selecting an attribute. You could select its parent

Rule/@action="Required"/..
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but it's more typical (and flexible) to uses a subquery

Rule[@action="Required"]
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If you're familiar with SQL, square brackets are kinda like an SQL WHERE clause.