These are created when Dynamic (or Input) Text is selected and the 'Target' checkbox is left unchecked.
A variable of the same name as the Text Object is automatically created for these Objects.
Text can be read and written to and from the Text Field via the associated variable of the same name.
Sample
trace(txtsimple); // displays "simple text object" the default text
txtsimple = "this is some different text"; // assigns new text to the Text Object
No other Text Field properties are available, e.g. txtsimple._X is not defined.