The first thing I was tasked with after I moved full time to the Zend Framework team (17 years ago! Yikes!) was to create a forms library. Like all the work I did for ZF in the early days, I first created a working group, gathered requirements, and prioritized features. There were a lot of requests:

• Ability to normalize values
• Ability to validate values
• Ability to get validation error messages
• Ability to render HTML forms, and have customizable markup
• Ability to do nested values
• Ability to handle optional values
• Ability to report missing values

and quite a lot more. But those are some of the things that stuck out that I can remember off the top of my head.

Zend_Form was considered a big enough new feature that we actually bumped the version from 1.0 to 1.5 to call it out.

And, honestly, in hindsight, it was a mistake.