If you were ever confronted with developing consistent and secure forms for html4 and/or xhtml you may have noticed that these are some inconsistent, over-complicated beasts, that require your meager brains to keep track of dozens of little specials and details, that make writing forms a royal pain in the buttocks.
So, how would HtmlForm change anything here? Well, first of all you can actually program your form with this instead of doing bit by bit handywork, rabidly switching between markup, parameter-parsing and algorithm. That's already a great thing for starters. But hey, there's more to come (in form of a list)!
HtmlForm does the following things, that you normally get paid to do:
complete (chainable) OO-wrapping for forms, and everything included in them
streamlined valuesets as submit-returns, where all widgets always return useful information and won't follow their own exotic set of rules
complete auto-handling for utf-8 values (if utf-8 is set up in php as shown in the overview)
auto-masking and value security including anti-magic-quote-measures
auto-refilling and easy default values for all widgets
nice, flexible and clean html-structure-output, to be easily adapted to fit most designs
Inclusion and Extension
Besides these pristine achievements it's fairly programmer-friendly as well:
the whole framework needs exactly one include, after which the framework is fully usable
there are no exotic plugins needed, every php 5.2.x standard installation should suffice (mbstring is needed for utf-8 processing, but that should be present in 99% of all cases)
adding new widgets and validators isn't rocket science, if you can write a class, you can do both