The HTML_Common2 package provides methods for HTML attributes handling and setting document-wide options. It is quite helpful as a building block for packages generating HTML and is used as such by HTML_QuickForm2 package. Main features:
Allows easy setting, removing, merging of HTML attributes, working with CSS classes;
Provides means to parse and generate HTML attribute strings;
Global document options: charset, linebreak and indentation characters;
Methods to handle indentation and HTML comments (useful in subclasses).
Note that HTML_Common2 is an abstract class, so you would probably subclass it and use a instance of a child class rather than HTML_Common2 itself. One notable exception is using its static methods to get and set global document options.