Is it valid to have a html form inside another html form?

Question

Is it valid html to have the following:

Answer 1

No, it is not valid. But a "solution" can be creating a modal window outside of form "a" containing the form "b".

    
        
        
        
        Save
    



    
    Open modal b 
    

It can be easily done if you are using bootstrap or materialize css. I'm doing this to avoid using iframe.