Drupal APIs

Render API

Drupal 8's Render API roughly consists of two parts:

The render pipeline — which is format-agnostic (HTML, JSON, anything)
Render arrays, which are a representation of a HTML page. They allow nesting (like HTML) and altering (necessary for Drupal's flexibility)

This guide provides comprehensive detailed information about both.

Short version in the API documentation: Render API overview: Caching

The parent page explains cacheability in general. This looks in detail at how render arrays bubble cacheability.

Drupal 8's Render API automatically creates placeholders of highly dynamic parts of a page, to have the best possible cacheability.

"Render Arrays" or "Renderable Arrays" are the building blocks of a Drupal page.

Render elements (including form input elements) in Drupal

How Drupal renders pages