DateTime::Format::Builder creates DateTime parsers. Many string formats of
dates and times are simple and just require a basic regular expression to
extract the relevant information. Builder provides a simple way to do this
without writing reams of structural code.

Builder provides a number of methods, most of which you'll never need, or at
least rarely need. They're provided more for exposing of the module's innards
to any subclasses, or for when you need to do something slightly beyond what I
expected. 

WWW: http://datetime.perl.org/