[galaxy-user] New Tool Question - how to copy meta data from input to output?

Hello, I'm writing a tool which accepts interval files and output interval files. The input file has the metadata set (chr/start/end columns). How can I copy the metadata to the generated output file? Currently, the output file's metadata is always set to chrom=1, start=2, end=3 (which I guess is the default for BED format). Other galaxy tools do it, so I'm sure it's possible. Which python code is responsible for that (to be included in my tool's XML) ? Thanks, Gordon.