Change attributes of <htmlb: form> in OnInputProcessing

I would like to change the value of <htmlb:form target='_blank'> in the OnInputProcessing.

How can I do it? I've found the CL_HTMLB_FORM but I didn't find any methods or attributes which I could use for this purpose.

Can anyone help me? It's urgent!

Thank You!

Kind Regards: Pal Halasz