reset element height to default dymanic behaviour

[ridou]

Hi,
I would like to reset the height of an element to the default value, ie "undefined". Let me explain a bit more:
When you start off with an element, for example a div, the height is dynamic. You fill it with some text and then you can retreive the height value from offsetheight.
Now if you set the height manually, with the style height, the height is now fixed. From there how do I come back to the dynamic behaviour ?
A wild guess would be to set the value style height value to "undefined".:x....