title: what is the red arrow on the left of the line numbers in Sublime
body: <p><a href="https://i.stack.imgur.com/FiyG0.png" rel="noreferrer"><img src="https://i.stack.imgur.com/FiyG0.png" alt="see the red arrow on the left of the picture" /></a></p>
  <p>What does the red arrow mean in Sublime Text editor between line 13 and 14?</p>