peterc,
This is a badly worded title for the question you are actually asking. I would consider the node and suggest an alternative, but unfortunately I have no idea what module you are using here.

Typically, the documentation for the module that $line is would tell you what public methods are available. Common sense would say if there is a get method, the set method, if there was one, would be set.

If this is not the case there is a way to access the object's internal structure directly (not through accessor or mutator methods), but that is typically frowned upon. You will need to look at the source or at least tell us what module you are using.