Extensible Template: Template engine extensible using sub-classes

This class implements a template processing engine.

It find and process tags in a template in the form of <tpl:TAG param1="value1" param2="value2" ...> block </tpl:TAG> or as in the contracted form <tpl:TAG param1="value1" param2="value2" ... />.

Each tag found is processed by calling functions of the class. Therefore, the template engine can be extended by a sub-class that implements new types of tags.

Currently the base class implements tags for replacing variables, iterating over loop blocks, generating HTML select, radio and checkbox tags, and including external template blocks.