Problem

This is a normal heredoc example.

let text =<< trim END
  if ok
    echo 'done'
  endif
END

If we wants new flags like eol other than trim,
the existing code like below will not work.

" eol is not flag!
let text =<< trim eol
  if ok
    echo 'done'
  endif
eol

Or some useful flags if available

• trim_left: if specified, trim only left
• trim_right: if specified, trim only right
• template: if specified, template string can be used in heredoc (Support 'template string' ('string interpolation') #4634)
• escape(chars): if specified, specified characters are escaped by backslash

Solution

• Make flags is lowercase letters only
• Make marker is uppercase letters only (if omitted, "." is used)

It gets rid of ambiguity from :let-heredoc, and guarantees forward compatibility.

And, if possible, I would like marker to be required parameter.
Currently "." is used if omitted, but it may confuse users? 🤔

" oops! "END" is missing
let text =<< trim
  if ok
    echo 'done'
  endif
END