I'm studying on gene expression and regulation, and read that enhancers (as eukaryotic promoter/regulatory elements) have the most variable position with respect to the start site of transcription. It says that there are a few reasons; enhancers can be upstream or downstream of the transcription start site and can exert their effect from hundreds or thousands of bases away. Plus, enhancers are "orientation-independent". What does "orientation-independent" mean?