title: Regex option "Multiline"
body: <p>I have a regex to match date format with comma.</p>
  
  <blockquote>
    <p>yyyy/mm/dd or yyyy/mm</p>
  </blockquote>
  
  <p>For example:</p>
  
  <blockquote>
    <p>2016/09/02,2016/08,2016/09/30</p>
  </blockquote>
  
  <p>My code:</p>
  
  <pre><code>string data="21535300/11/11\n";
  Regex reg = new Regex(@"^(20\d{2}/(0[1-9]|1[012])(/(0[1-9]|[12]\d|30|31))?,?)*$", 
                        RegexOptions.Multiline);
  
  if (!reg.IsMatch(data))
      "Error".Dump();
  else
      "True".Dump();
  </code></pre>
  
  <p>I use option multiline.
  If string data have "\n".
  Any character will match this regex.</p>
  
  <p>For example:</p>
  
  <pre><code>string data="test\n"
  string data="2100/1/1"
  </code></pre>
  
  <p><a href="https://msdn.microsoft.com/zh-tw/library/yd1hzczs(v=vs.110).aspx#Multiline" rel="nofollow">I find option definition in MSDN</a>. It says:</p>
  
  <blockquote>
    <p>It changes the interpretation of the ^ and $ language elements so that they match the beginning and end of a line, instead of the beginning and end of the input string.</p>
  </blockquote>
  
  <p>I didn't understand why this problem has happened.
  Anyone can explan it?
  Thanks.</p>