Looking for actual routine that phptemplate uses.

This is something I know phptemplate does, ie it takes a string containing text with blocks, a list of php variables, or perhaps all the variables in scope and replaces all the occurrences of the php blocks with the value when evaluated.

Essential it is $output = function($inputStringContainingPhpBlocks, $currentVariableBinding)

For those familiar with Ruby it is like Erb.new with the current binding.

What is name of the function that accomplishes this?