If I understand the Designer 8.0 help files, they indicate that you can specify a subform that is already part of your original page to be an overflow header to appear on subsequent pages for a flowed object. The help file gives the example that you could repeat the heading row of a table on subsequent pages.
In my case, I have a large text field where users respond to a long open-ended question. I have a block of text that goes on the first page explaining what information the user must include in their response. When the text field overflows, I want it to spill onto subsequent pages, which I have finally figured out how to do.
However, I would like (need?) to have a header placed ONLY on subsequent pages (not the first page) to indicate that these are continued pages. For instance, assume my heading for the original text field looks like the following:
Miscellaneous: Use this space to provide any information for which there was not sufficient space in any other sections of the form. For each such item of information clearly identify the item number that the information belongs to. Your response is not limited to one page. Additional page(s) will automatically be inserted into this form if the length of your response exceeds the space on this page.
For subsequent pages, I want a heading that just says the following:
Here I assume I would need to have a subform with a text object whose string was simply "Miscellaneous (continued)," and I would specify this as my overflow header. The problem is that I do NOT want this subform to appear UNLESS there is an overflow. How can I specify an overflow header to only be the overflow header on pages created by an overflow? Is there a place I can put subforms that won't show up in the document, so that they will only be visible if there is an overflow?
This is kind of tricky. You want a client-side dynamic subform that grows in response to user input. In my opinion, data binding and flowed subforms are not really intended to be used this way. The power of XFA is realized when data is bound to an XDP on the server and the result is a PDF that 'grows' to accomodate the data dynamically.
Having said that, I know there are lots of forms out there that are built to do exactly what you are looking for but I have not built one. I suspect you will have to keep track of the character count on the text field and then force pagination.
Regarding the heading issue, you can create two master pages, 'Page1' with the full text and 'Page2' with the abbreviated text. On the subform containing the text field, go to the Pagination tab and change 'If Dataset Must Be Paginated: Overflow' to "Go To Page 'Page2'".
If I understand you it is a field that is overflowing and not a subform (even though the field is in a subform). Hence the header subform stuff will not apply in this case. The field will try to take up all of the space on the page so you cannot even add the text that you want. What if we had a string in the Masterpage header area and had it as invisible, then if we could determine that the field broke across pages we could set that instance of the text to visible.