This is not something I've encountered frequently and I haven't come many people who've had this problem either, making it a little more perplexing when you do encounter it. Imagine having an XML Form with over 20 entry fields, if you have to fill out each field every time you create a form it could be quite frustrating for end users to have to click on each field with their mouse, so obviously the tab key will make this easier, but what if this doesn't work?
E.g. you have a large XML Form in which the tab key doesn't work:
This is generally browser specific and normally only occurs in Internet Explorer. IE is unable to handle the complex HTML tables that are created when rendering such a large XML Form which results in the tabbing functionality not working.
The solution here is in some ways a little obvious, which is maybe why it doesn't come up too often. You need to avoid too much overlapping of your controls as this leads to more complex HTML tables, e.g.
Try to arrange your controls more like a table with less columns, e.g.
Unfortunately there is no concrete workaround to actually resolve this issue however, at least if you know the reason it happens you can play around with your Edit Form to make sure this works before making the XML Form publically available to end users.
