Show {expr} inside the balloon. For the GUI {expr} is used as a string. For a terminal {expr} can be a list, which contains the lines of the balloon. If {expr} is not a list it will be split with balloon_split(). If {expr} is an empty string any existing balloon is removed.

Example:

func GetBalloonContent()
   " ... initiate getting the content
   return ''
endfunc
set balloonexpr=GetBalloonContent()

func BalloonCallback(result)
  call balloon_show(a:result)
endfunc

Can also be used as a method:

GetText()->balloon_show()

The intended use is that fetching the content of the balloon is initiated from 'balloonexpr'. It will invoke an asynchronous method, in which a callback invokes balloon_show(). The 'balloonexpr' itself can return an empty string or a placeholder, e.g. "loading...".

When showing a balloon is not possible then nothing happens, no error message is given. only available when compiled with the +balloon_eval or +balloon_eval_term feature