Zend Anwar

It inherints directly from Mage_Core_Block_Abstract and extends its base class only with three methods:

1.  public function setText($text)
2.  public function addText($text, $before=false) {}
3.  public function getText()

The block only stores a text string (it could be plain or html of course), and during rendering phase, the block simply outputs the stored string.

You could set the string to a value or append / prepend the text to the existing string.