\version "2.27.1"

% I usually print on Letter paper:
#(set-default-paper-size "letter")

\paper {
%  left-margin = 15\mm
%  right-margin = 15\mm
% I *think* the default margins are 15mm,
% even when I am using letter paper?
% https://github.com/lilypond/lilypond/blob/master/ly/paper-defaults-init.ly
}

\markup \bold { A justified paragraph
  in LilyPond, uninformed by LaTeX:
}
\markup \null

% If needed, specify \abs-fontsize
% (the default is #11)
\markup \justify {
  LilyPond came about when two musicians wanted to go
  beyond the soulless look of computer-printed sheet music.
  Musicians prefer reading beautiful music, so
  why couldn’t programmers write software
  to produce elegant printed parts?
  The result is a program that creates beautiful sheet music
  following the best traditions of classical music engraving.
  The best thing about LilyPond is that it handles all layout
  programmatically, allowing composers, transcribers
  and publishers to focus on the music instead of
  improving their software’s default output.
}

\markup \vspace #1
\markup \bold { A justified paragraph
  in LilyPond, with manual hyphenation taken from LaTeX output:
}
\markup \null

\markup \justify {
  LilyPond came about when two musicians wanted to go
  beyond the soulless look of computer-printed sheet music.
  Musicians prefer reading beautiful music, so
  why couldn’t programmers write software
  to produce elegant printed parts?
  The result is a program that creates beautiful sheet music
  following the best tradi-
%%% MANUAL LINE BREAK HERE %%%
  tions of classical music engraving.
  The best thing about LilyPond is that it handles all layout
  programmat-
%%% MANUAL LINE BREAK HERE %%%
  ically, allowing composers, transcribers
  and publishers to focus on the music instead of
  improving their software’s default output.
}