label: The configured label of the block if visible.
configuration: A list of the block's configuration values.
label: The configured label for the block.
label_display: The display settings for the label.
provider: The module or other provider that provided this block plugin.
Block plugin specific settings will also be stored here.
content: The content of this block.
attributes: HTML attributes for the containing element.
id: A valid HTML ID and guaranteed unique.
title_attributes: HTML attributes for the title element.
content_attributes: HTML attributes for the content element.
title_prefix: Additional output populated by modules, intended to be
displayed in front of the main title tag that appears in the template.
title_suffix: Additional output populated by modules, intended to be
displayed after the main title tag that appears in the template.
Headings should be used on navigation menus that consistently appear on
multiple pages. When this menu block's label is configured to not be
displayed, it is automatically made invisible using the 'visually-hidden' CSS
class, which still keeps it visible for screen-readers and assistive
technology. Headings allow screen-reader and keyboard only users to navigate
to or skip the links.
See http://juicystudio.com/article/screen-readers-display-none.php and
http://www.w3.org/TR/WCAG-TECHS/H42.html for more information.