The function is called `webvtt_string_is_equal`

It's important to note that if the length of the comparison string is not equal to the length of the string, in bytes, the function will return false. For instance:

webvtt_string str // This string contains "Hello"
const char *str2 = "Hello World!";
webvtt_string_is_equal(&str,str2,-1); // This returnse false (0) even though "Hello World!" starts with the contents of str.

Apart from this, the demo is a bit unrealistic. It would be something more like:

```C
if( webvtt_string_is_equal( &str, "SDP-US", -1 ) ) {
  // We got an SDP-US token! Do something special!
} else {
  // Behave as normal!
}
```

Just a really simple demonstration of how it works.