documentation: keys and use-cases

Hi,
I don't understand the use-case.
Let's say an application is using this library before submitting something to a remote server.

The "key" in this context would be the "public key" of the captcha. You confirm?
Then the g-response-message (that this library take care of) is going to be submitted to the server which will use it's secret key to verify the captcha. Still right?
In this context what means ReCaptchaDomain?
Sample show recaptcha?.validate(), what means "validating" in this context?
Sample use a webview.frame is it still compatible with native app' not relying on webview?

thx!

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