The outlining capability in Coda is SO useful 
Yet it stops short - see Is there a keyboard shortcut to expand/collapse just one toggle/collapsable list at a time? - #4 by Jean_Pierre_Traets
Can you provide a shortcut key to expand and collapse one level at a time, with a shortcut key. CMD . (period) is what OneNote uses for example. (OneNote has some of the best outlining capabilities and so please try them for reference)
Can you enable these for headings as well as regular collapsible lists
Thank you!