Text_CAPTCHA provides information about the CAPTCHA and makes its inner workings accessible using several functions defined in the base class; the specific implementation of them is up to the driver.
init() is used to initialize the CAPTCHA and provide further information, like Image_Text parameters.
_createCAPTCHA() generates the CAPTCHA, but is called internally by init().
getPhrase() returns the CAPTCHA's phrase.
_createPhrase() creates a phrase for the CAPTCHA, but is used internally.
getCAPTCHA() returns the CAPTCHA, the format used depends on the driver implementation.