Can we use html4 and html5 at the same time?

Question

a .html file that contain html4 and html5 tag

Answer 1

Since most browser keeps HTML standard backwards compatibility I guess you can mix them together, however if you want to validate your file with HTML5 standard you may get some notes, about the mixture of HTML 4 & 5.

Answer 2

help me python coding please
2 question more at my home
thank you for your help