class YARP::LexCompat::Heredoc::DedentingHeredoc

def <<(token)

remove that amount of whitespace from the beginning of each line.
whitespace on plain string content tokens. This allows us to later
As tokens are coming in, we track the minimum amount of common leading 
def <<(token)
  case token.event
  when :on_embexpr_beg, :on_heredoc_beg
    @embexpr_balance += 1
  when :on_embexpr_end, :on_heredoc_end
    @embexpr_balance -= 1
  when :on_tstring_content
    if embexpr_balance == 0
      token.value.split(/(?<=\n)/).each_with_index do |line, index|
        next if line.strip.empty? && line.end_with?("\n")
        next if !(dedent_next || index > 0)
        leading = line[/\A(\s*)\n?/, 1]
        next_dedent = 0
        leading.each_char do |char|
          if char == "\t"
            next_dedent = next_dedent - (next_dedent % TAB_WIDTH) + TAB_WIDTH
          else
            next_dedent += 1
          end
        end
        @dedent = [dedent, next_dedent].compact.min
      end
    end
  end
  @dedent_next = token.event == :on_tstring_content && embexpr_balance == 0
  tokens << token
end