Render Array Standard Keys

Borrowed from the Drupal 8 API Documentation.

Property	Description
`#type`	The element type. If this array is an element, this will cause the default element properties to be loaded, so in many ways this is shorthand for a set of predefined properties which will have been arranged through a `RenderElement` plugin. The Drupal 8 API docs has a full list of available element types.
`#cache`	Mark the array as cacheable and determine its expiration time, etc. Once the given render array has been rendered, it will not be rendered again until the cache expires or is invalidated. Uses the Cache API. This property accepts the following subproperties: `'keys'` `'contexts'` `'tags'` `'max-age'` `'bin'` See Cacheability to learn more. It's very important to set `#cache` correctly!
`#markup`	Specifies that the array provides HTML markup directly. Unless the markup is very simple, such as an explanation in a paragraph tag, it is normally preferable to use #theme or #type instead, so that the theme can customize the markup. Note that the value is passed through \Drupal\Component\Utility\Xss::filterAdmin(), which strips known XSS vectors while allowing a permissive list of HTML tags that are not XSS vectors. (I.e, `<script>` and `<style>` are not allowed.)
`#plain_text`	Specifies that the array provides text that needs to be escaped. This value takes precedence over #markup if present.
`#prefix`/`#suffix`	A string to be prefixed or suffixed to the element being rendered
`#pre_render`	An array of functions which may alter the actual render array before it is rendered. They can rearrange, remove parts, set `#printed = TRUE` to prevent further rendering, etc.
`#post_render`	An array of functions which may operate on the rendered HTML after rendering. A `#post_render` function receives both the rendered HTML and the render array from which it was rendered, and can use those to change the rendered HTML (it could add to it, etc.). This is in many ways the same as `#theme_wrappers` except that the theming subsystem is not used.
`#theme`	A single theme function/template which will take full responsibility for rendering this array element, including its children. It has predetermined knowledge of the structure of the element. See hook_theme and Theme system overview.
`#theme_wrappers`	An array of theme hooks which will get the chance to add to the rendering after children have been rendered and placed into `#children`. This is typically used to add HTML wrappers around rendered children, and is commonly used when the children are being rendered recursively using their own theming information. It is rare to use it with `#theme`.
`#sorted`	TRUE if the elements of this render array have been sorted by weight. You can set this to FALSE to force Drupal to re-sort the elements in the array. This is useful when adding a new element to a render array in a preprocess hook.