Why would the compiler generate a `"E2018 Record, object or class type required" helper` when I use a ToUpperInvariant (or any TStringsHelper call) on the `Text` property of a `TEdit`?

Why would the compiler generate a `"E2018 Record, object or class type required" helper` when I use a ToUpperInvariant (or any TStringsHelper call) on the `Text` property of a `TEdit`?

Full failing code is at https://gist.github.com/jpluimers/b5e3684f725216622bdcb80bf5f10698

Failing line is this:

```
Edit1.Text := Edit1.Text.ToUpperInvariant;
// the above line generates this error:
// [dcc32 Error] MainFormUnit.pas(29): E2018 Record, object or class type required
```

This fails as well:

```
Edit1.Text := TStringHelper.ToUpperInvariant(Edit1.Text);
```

Why would the compiler (in this case XE8) throw this error?

Note the workaround is simple:

```
var
lText: string;
begin
lText := Edit1.Text;
Edit1.Text := lText.ToUpperInvariant;
```

My suspicion is that the `Edit` property is of type `TCaption` which is `type string`.

Could it be that simple?