vim/after/ftplugin/markdown.vim @ dcd072c2fbb6

" folding for Markdown headers, both styles (atx- and setex-)
" http://daringfireball.net/projects/markdown/syntax#header
"
" this code can be placed in file
"   $HOME/.vim/after/ftplugin/markdown.vim

func! Foldexpr_markdown(lnum)
    let l1 = getline(a:lnum)

    if l1 =~ '^\s*$'
        " ignore empty lines
        return '='
    endif

    let l2 = getline(a:lnum+1)

    if  l2 =~ '^==\+\s*'
        " next line is underlined (level 1)
        return '>1'
    elseif l2 =~ '^--\+\s*'
        " next line is underlined (level 2)
        return '>2'
    elseif l1 =~ '^#'
        " current line starts with hashes
        return '>'.matchend(l1, '^#\+')
    elseif a:lnum == 1
        " fold any 'preamble'
        return '>1'
    else
        " keep previous foldlevel
        return '='
    endif
endfunc

setlocal foldexpr=Foldexpr_markdown(v:lnum)
setlocal foldmethod=expr

"---------- everything after this is optional -----------------------
" change the following fold options to your liking
" see ':help fold-options' for more
setlocal foldenable
setlocal foldlevel=0
setlocal foldcolumn=0