Built-in variables are a special category of variables that are predefined and cannot be customized. When you create a new container, it initially contains no user-defined variables, but some built-in variables are already enabled. These enabled built-in variables are accessible across ClickFlare Tag Manager whenever variable selection menus are present.

You can access the list of built-in variables, directly from the tags or triggers' section of the container.

To check built-in variable from tag configuration:

1. Click on + New Tag
2. Select a tag configuration, like Custom Event for example 
3. Next to the variable placeholder, click on the "+" symbol
4. Go through the list of built-in variables

You can do the same from the trigger's configuration.

Related Sources:

• Built-in variables
• User-defined variables
• User-defined variables types
• About variables