Form validation

I am creating a plugin that need a few forms for adding custom data to my database.

I’d obviously like it to look like a WordPress form and act as such.

Is there any documentation on the correct (or best) way to implement a form in terms of HTML and CSS?

More importantly, is there a inbuilt WP validation library?

I was looking at the “Add New User” form and would like to replicate the validation used there, but I cannot figure it out. I have used the same CSS classes for parts of the form but I’m getting nowhere.

Is this even possible, or should I give up and just use my own validation?