Twilio relies on your web app to supply it with instructions about how to direct calls and text messages. This is done via webhooks - synchronous HTTP callbacks Twilio makes to your app with status on the call and information about the caller.
One of the most powerful features of Twilio is TwiML, the XML-based instruction language that lets your app respond to webhooks from Twilio with directions on how to proceed with the call. As long as your app can speak normal HTTP and emit an application/xml response, your app can speak TwiML. <Dial> the caller to a second phone number, <Conference> users together, <Record> audio, and much more. All facilitated by webhooks and your app logic.
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