I would like to ask, if someone has an idea how to go through accessibility problem with javascript date pickers, when is used tabindex attribute in form.
When you add tabindex to set order of inputs in form, then is not possible to get
to datepicker , which is nextSibling to appropriate inputs. I try few solutions, best seems this:

function nextTab(el){
But it not works well, on first focus and I dont have idea why. I see that I could rewrite all tabindex after those affected input with date picker, but it is a lot of code. I am not sure also about tabindex. Is it problem to have html tabindex order like 1,2,3,4,6,8 and leave form without tabindex 5 and 7, when javascript is off? (I mean tabindex 5 and 7 will be at elements added by javascript, so question is what happen when I tab from 4 to 6, when 5 is not there?). I dont know how to explain it better. Example is here http://www.kongresove-sluzby.cz/poptavka.php in the middle of form.