Casper: purpose of site-header and site-nav-main, navigation loaded twice?

I am trying to understand and adapt the Casper theme, and I am wondering why the site-nav partial is imported twice in index.hbs: once at the very beginning, and once further down via the site-header partial.

This are the two lines I am talking about:

  1. https://github.com/TryGhost/Casper/blob/b51dd8ce22cfbf4c8b833f2bdf0d0793e31a5d26/index.hbs#L8
  2. https://github.com/TryGhost/Casper/blob/b51dd8ce22cfbf4c8b833f2bdf0d0793e31a5d26/index.hbs#L39

I cannot see any difference. In fact, I have removed the site-header partial in a local ghost instance and did not observe a difference in looks or behaviour. To me it appears the the sole difference between both navigations is that one is part of a div with classes outer and site-nav-main.

Is this an oversight or is there a deeper reason for loading the same partial twice?

Just as I submitted the question, I realized what’s different: when scrolling down, the second navigation is loaded in.

Very cool effect.