Runway shares the tag-based template language with Perch, with some extensions for Runway-specific features.
When a page function outputs content, it does so using a template. A template is a fragment of (usually) HTML that contains tags defining the different content fields in use.
<h1> <perch:content id="title" type="text" label="Title"> </h1> <p> Published on: <perch:content id="published_on" type="date" label="Date" format="d F Y H:i"> </p>
Everything that is output from a page function is done so through a template. Templates are custom to your site and contain whatever markup your site needs. They are usually HTML, but can output any type of text format.
Visit the template reference.