I think you are referring to the OSIsoft.AF.UI Namespace, which is a Microsoft .NET assembly that provides structured access to .Net windows controls for displaying and interacting with AFSDK objects. The AF UI objects are designed to be used in Windows Forms. You might be able to use some of the objects if you are developing a .NET based web application (e.g. ASP.NET), but there are some limitations (e.g. you will need .NET installed on client machines).
If you are not developing a .NET based web application (since you mentioned PHP/HTML5, etc.), perhaps you can build custom UI components and use PI Web API to interact with the PI system.