title: Term for a "Special Identifier" Embedded in String Data
body: <p>I'm mostly at a loss for how to describe this, so I'll start with a simple example that is similar to some JSON I'm working with:</p>
  
  <pre><code>"user_interface": {
      username: "Hello, %USER.username%",
      create_date: "Your account was created on %USER.create_date%",
      favorite_color: "Your favorite color is: %USER.fav_color%"
  }
  </code></pre>
  
  <p>The "special identifiers" located in the <code>username</code> <code>create_date</code> and <code>favorite_color</code> fields start and end with <code>%</code> characters, and are supposed to be replaced with the correct information for that particular user. An example for the <code>favorite_color</code> field would be:</p>
  
  <p><code>Your favorite color is: Orange</code></p>
  
  <p>Is there a proper term for these identifiers? I'm trying to search google for best practices or libraries when parsing these before I reinvent the wheel, but everything I can think of results in a sea of false-positives.</p>