To automate a website, you may first want to inspect it. For that you can use our Form Utility application to show which form fields are available. The application suggests which commands to use to query or set fields. Then you can use WebView.SetFormButtonValue, WebView.SetFormInputChecked, WebView.SetFormInputValue, WebView.SetFormSelectValue, WebView.SetFormTextAreaValue and WebView.SetFormValue to change form fields.
For MacOS and iOS in FileMaker 16 or newer you can use WebView.SetPreferences function to set preferences for developer extras and show the inspector in the web viewer.