Drupal 7 Module Development

Lastly, the kitten element's #type property is set to link. The #type property
tells drupal_render() how to render that element. When we learn about
hook_element_info(), we'll understand why, but for now drupal_render()
will pass the kitten element to the drupal_pre_render_link() function which
will render the element using l() and return its output.
Chapter 3
Render properties
Render element properties are defined in two places. The first place where properties
are defined is directly inside drupal_render() and its helper functions. The
following is a complete list of properties used by drupal_render():
• #access: A Boolean indicating if the current user has access to view
the element.
• #cache: An array indicating whether the element should optionally
be retrieved from cache or stored in cache after rendering. See
drupal_render() for more information.
• #markup: A string containing markup (such as HTML). If this property is
set, the #type property does not need to be set, as it will automatically be
set to markup.
• #type: A string indicating which element is being rendered. The default
properties for this type of element are extracted from the data specified
with hook_element_info() and merged with the render element.
• #defaults_loaded: A Boolean indicating whether the element type's default
properties have already been loaded. If this is false or not set, the default
properties from element_info() are added before drupal_render() looks
at any other render properties (except for #access and #cache).
• #pre_render: An array of callbacks to apply to the element before theming.
• #theme: A string specifying the theme hook to be used on the element.
• #theme_wrappers: An array of theme hooks to be used on the element after
initial theming and/or after the child elements have been rendered. Theme
functions that are to be used as wrappers need to be specially written to look
for the #children property in the render element passed to it from theme.
• #post_render: An array of callbacks to apply to the element after theming.
• #children: The rendered element and its children. It is normally built up
internally by drupal_render() as it renders the elements, but can also be
set by a #pre_render callback.
• #prefix: A string containing markup to be prepended to the
#children property.
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