It's often useful to transform raw values in some way, and this is achieved in IPS4 with template plugins. Template plugins take a value, and optionally some arguments, and output some transformed value.
The syntax for template tags is:
{pluginkey="<value>" argument="..."}
The value can be a normal string, or it could be a variable coming from elsewhere.
Template plugins can always be used in templates, but some can also be used in CSS files. Those that can are identified