Drupal 8 hook arguments

content.md

$content[field_machine_name] =>
  0,
  1,
  2,
  #theme,
  #title,
  #label_display,
  #view_mode,
  #language,
  #field_name,
  #field_type,
  #field_translatable,
  #entity_type,
  #bundle,
  #object,
  #items Drupal\Core\Field\EntityReferenceFieldItemList,
  #formatter,
  #is_multiple,
  #cache,
  #weight

0 => 
  #theme,
  #node,
  #view_mode,
  #cache,
  #weight,
  #pre_render

hook_preprocess_node.md

array $variables

Key	Type
elements	array
theme_hook_original	string
attributes	array
title_attributes	array
content_attributes	array
title_prefix	array
title_suffix	array
db_is_active	boolean
is_admin	boolean
logged_in	boolean
user	Drupal\Core\Session\AccountProxy
directory	string
view_mode	string
teaser	boolean
node	Drupal\node\Entity\Node
date	Drupal\Core\Render\Markup
author_name	Drupal\Core\Render\Markup
url	string
label	array
page	boolean
content	array
author_attributes	Drupal\Core\Template\Attribute
display_submitted	boolean
#cache	array

hook_preprocess_paragraph.md

array $variables

Key	Type
elements	array
theme_hook_original	string
attributes	array
title_attributes	array
content_attributes	array
title_prefix	array
title_suffix	array
db_is_active	boolean
is_admin	boolean
logged_in	boolean
user	Drupal\Core\Session\AccountProxy
directory	string
view_mode	string
paragraph	Drupal\paragraphs\Entity\Paragraph
content	array
#cache	array