How does iXBRL work in practice

Hello there. I'm hoping someone can help me fill a gap in my knowledge.  I'm currently studying ATT and I know that companies now have to file their Corporation Tax Returns electronically and provide accounts and computations in iXBRL format.  I'm not currently getting any practical tax experience though, so I don't know what that means in practical terms.

My questions essentially are:

1. Can you make whitespace disclosures within the computations using iXBRL?
2. Can you attach any additional documents?

One situation that I'm thinking of in particular (and I expect there are others) is the making of R&D claims.  HMRC's guidance says, "Although it's not a legal requirement, HMRC encourages companies and organisations to:

• tell them why the company or organisation considers its project(s) to be allowable as R&D (as defined in the section above)
• provide a summary of the costs incurred on the R&D and how the figures in the return were arrived at."

I just wondered how you would achieve that in real life.  Can you make a whitespace disclosure? can you attach some sort of report or similar in pdf format?