What: Create a split window in Vim with arbitrary content
Why: Displaying information easily along text your are editing
How: Use Vimscript

A simple Vimscript script

Create a file test.vim with the following content. It defines a function which creates a new buffer, adds text to it and show it in a split window on the right.

function! test#test()
  let buffernum = bufadd("")
  call bufload(buffernum)
  call setbufline(buffernum, 1, "Hey ho")
  execute "vertical rightbelow sb " . buffernum
endfunc

Use the defined function

There are multiple ways, the function can be used. You can create a plugin (see https://learnvimscriptthehardway.stevelosh.com/chapters/41.html) or call the function from within Vim:

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:source test.vim
:call test#test()