How to specify the range of possible values for font-s

Hello!

We're working on a simple copyfitting implementation based on FOP1.0
and XSL-FO 2.0 specification.And we want our extension to fit
completely to the specification.

Due to copyfitting task we need to use font-size and line-height as
adjustable-attributes and we need to limit both of them by minimum and
maximum values.

It's fine for line-height - it's possible to use line-height.minimum
and line-height.maximum. But font-size is not defined as range(space)
attribute in specification, so if we want our implementation fit to
specification we cannot use font-size.minimum and font-size.maximum.

Are there any ways to set range of values for font-size attribute?

Kind Regards,
Alexander