Today i have problem give the tabindex to the Contact form which is set using the Powermail in Typo3.
First R&D on this and get idea to set it from the Contact Editor.
In Contact Editor Select Plugin.Powermail_Addinitional_Config and add the uid of the elements using in th form as Textbox, Textarea, Radio button, Checkbox etc.
I got success to set the tabindex manually from backend using the contact editor. See the Screenshot.
Define the uid in this “Manual sorting of tabindex[plugin.powermail.barrier-free.tabindex]”..
if you got the problem with any uid for exa: “check_uid27_0” like this please remove prefix “check_” and only save “uid27_0” and problem is solved.