Handling nested formular data

Hi,

it'll be my job to create formulars where the given information can be strutured. There's not only value1=x, value2=y, value3=z, but also value1=x, value1_a=y, value1_b=z and so on. I'm asking myself whether it's good to save those meta informationen in the formular data anyhow or to have a kind of parser, which structures the information given by the formular data on the basis of a predefined syntax definition and validates the incoming data with a state machine, for example. The problem is, I think, that a formular can easily be manipulated and thus an extra checking is necessary anyhow.

Thank you for any suggestions! ms