Visual constraints

Hi,
 
Could any one tell me if there is any support for constraining the
amount of text in a section of a document with XSL:FO? Given that I
don't have my head round the correct terminology yet (still evaluating
technologies) I'll explain this in English.
 
If I have a layout with a small area I want to somehow detect if the
text associated with it is too large to fit in the area and either drop
out with an error, add an error to the output file or flow the text into
another conditional area (probably another page) which I can detect
programmatically from the resultant file.
 
If anyone has any tips or references I'd appreciate it.
 
Thanks,
Steve