This class implements all functions necessary for highlighting,
but it does not contain highlighting rules. Actual highlighting is
done using a descendent of this class.
One is not supposed to manually create descendent classes.
Instead, describe highlighting rules in XML format and
use {@link Text_Highlighter_Generator} to create descendent class.
Alternatively, an instance of a descendent class can be created
directly.
Use {@link Text_Highlighter::factory()} to create an
object for particular language highlighter
Usage example
require_once 'Text/Highlighter.php';
$hlSQL = Text_Highlighter::factory('SQL',array('numbers'=>true));
echo $hlSQL->highlight('SELECT * FROM table a WHERE id = 12');