Strange implicit camel-case conversion when use both unknown-options-as-args and alias

Given code below:

const result = require("yargs-parser")(
  ["--foo", "bar", "--outDir", "dist"],
  {
    string: ["_", "foo", "out-dir"],
    configuration: {
      "unknown-options-as-args": true 
    }
  }
);

console.log(result);

This will print:

{ _: [ '--outDir', 'dist' ], foo: 'bar' }

In which outDir is parsed as a positional argument. This makes sense because outDir is not presented in string, even though its kebab-case variation presented.

However, when I set an alias for out-dir, It behaves in another way:

const result = require("yargs-parser")(
  ["--foo", "bar", "--outDir", "dist"],
  {
    string: ["_", "foo", "out-dir"],
    configuration: {
      "unknown-options-as-args": true 
    },
    alias: {
      "o": "out-dir"
    }
  }
);

console.log(result);

This will print:

{ _: [], foo: 'bar', outDir: 'dist', o: 'dist', 'out-dir': 'dist' }

In which the former unknown option outDir is parsed as a named argument now. I don't know if there are some implicit conversions under the hood?

If the camel-case conversion is intended, I hope the first example will treat outDir as a known named argument too.

Tested in the current version of yargs-parser@20.2.6

Start by running the two yargs-parser@20.2.6 examples from the issue and compare handling of unknown-options-as-args with the alias for out-dir. Trace the parser's alias and camel-case conversion paths to determine why --outDir changes classification. Done means the behavior is documented by a regression test and matches the intended handling of the camel-case option.