title: Strange character for empty line in TextWrangler and cat -v
body: <p>I have a text file, which on my Mac I open with TextWrangler. I enable the invisible characters to see the line endings. I see that every empty line has a red, upside down question mark in it. Which character is this?</p>
  
  <p>When in the terminal I type <code>cat -v file.txt</code>, it shows these characters as <code>^@</code> (and the line endings themselves as <code>^M</code>). What I need to know is the regex of that specific character, like <code>/n</code> for the end of line.</p>
  
  <p>In the hex dump, I see the following:</p>
  
  <pre><code>0000000: 312e 300d 0a00 0d0a 2231 3130 3030 3030  1.0....."1100000
  0000010: 3030 3222 3b22 3922 3b22 5354 4422 3b3b  002";"9";"STD";;
  0000020: 3b0d 0a22 3131 3030 3030 3030 3639 223b  ;.."1100000069";
  </code></pre>
  
  <p>If I manually remove the strange characters, and make a new hex dump, I see:</p>
  
  <pre><code>0000000: 312e 300d 0a0d 0a22 3131 3030 3030 3030  1.0...."11000000
  0000010: 3032 223b 2239 223b 2253 5444 223b 3b3b  02";"9";"STD";;;
  0000020: 0d0a 2231 3130 3030 3030 3036 3922 3b22  .."1100000069";"
  </code></pre>
  
  <p>The difference is a byte sequence 00. Is there an encoding in which this 00 is required for empty lines?</p>