Theme functions are used to render UI elements in a consistent way. There are theme functions defined for over 200 elements in Backdrop core, and while many of them are only used for special purposes, many others are used widely; all are available to developers.

Note that you should never call a theme function directly; instead of

$output = theme_something($variables);

you should call

$output = theme('something', $variables);

to allow for setting of default values, overrides, and modifications. See Default theme implementations for more details.

Function Location Summary
theme_indentation core/includes/theme.inc Returns HTML for an indentation div. Used for drag and drop tables.
theme_installer_browser_project_description core/modules/installer/installer.theme.inc Builds the truncated description on the project list.
theme_install_page core/includes/theme.maintenance.inc Returns HTML for the installation page.
theme_item_list core/includes/theme.inc Returns HTML for a list or nested list of items.
theme_label_machine_name core/modules/system/system.theme.inc Returns HTML for the display of a label and its machine name.
theme_language_admin_overview_form_table core/modules/language/language.theme.inc Returns HTML for the language overview form.
theme_language_negotiation_configure_form core/modules/locale/locale.theme.inc Returns HTML for the language negotiation configuration form.
theme_layout_action_links core/modules/layout/layout.theme.inc Output a list of action links for layouts.
theme_layout_conditions core/modules/layout/layout.theme.inc Output the list of visibility conditions for layouts.
theme_layout_condition_info core/modules/layout/layout.theme.inc Outputs a list of conditions. Used in the layout listing page.
theme_layout_flexible_template_style_option core/modules/layout/layout.theme.inc Outputs a representation of the column widths of a flexible layout template row.
theme_layout_info core/modules/layout/layout.theme.inc Outputs information about a layout. Used in the layout listing page.
theme_layout_menu_item_arguments_table core/modules/layout/layout.theme.inc Output the arguments table for layout_menu_item_arguments_form().
theme_layout_region_inner core/modules/layout/layout.theme.inc Output region content wrapped by tag specified in layout UI.
theme_layout_reorder_layouts core/modules/layout/layout.theme.inc Turn the rearrange form into a table with table sorting displayed.
theme_layout_settings_context_table core/modules/layout/layout.theme.inc Output the table for layout_settings_form() contexts.
theme_layout_template_info core/modules/layout/layout.theme.inc Outputs information about a layout template . Used in the layout template listing page.
theme_layout_template_option core/modules/layout/layout.theme.inc Outputs an individual option label for selecting a layout.
theme_link core/includes/theme.inc Returns HTML for a link.
theme_links core/includes/theme.inc Returns HTML for a set of links.
theme_link_field core/modules/link/link.theme.inc Formats a link field widget.
theme_link_formatter_link_absolute core/modules/link/link.theme.inc Formats a link as an absolute URL.
theme_link_formatter_link_default core/modules/link/link.theme.inc Formats a link.
theme_link_formatter_link_domain core/modules/link/link.theme.inc Formats a link using the URL's domain for it's link text.
theme_link_formatter_link_label core/modules/link/link.theme.inc Formats a link using the field's label as link text.
theme_link_formatter_link_plain core/modules/link/link.theme.inc Formats a link (or its title) as plain text.
theme_link_formatter_link_separate core/modules/link/link.theme.inc Formats a link as separate title and URL elements.
theme_link_formatter_link_short core/modules/link/link.theme.inc Formats a link using "Link" as the link text.
theme_link_formatter_link_title_plain core/modules/link/link.theme.inc Formats a link's title as plain text.
theme_link_formatter_link_url core/modules/link/link.theme.inc Formats a link using an alternate display URL for its link text.
theme_locale_date_format_form core/modules/locale/locale.theme.inc Returns themed HTML for the locale_date_format_form() form.
theme_mark core/includes/theme.inc Returns HTML for a marker for new or updated content.
theme_menu_admin_overview core/modules/menu/menu.theme.inc Returns HTML for a menu title and description for the menu overview page.
theme_menu_link core/includes/menu.inc Returns HTML for a menu link and submenu.
theme_menu_local_action core/includes/menu.inc Returns HTML for a single local action link.
theme_menu_local_actions core/includes/menu.inc Returns rendered HTML for the local actions.
theme_menu_local_task core/includes/menu.inc Returns HTML for a single local task link.
theme_menu_local_tasks core/includes/menu.inc Returns HTML for primary and secondary local tasks.
theme_menu_overview_form core/modules/menu/menu.theme.inc Returns HTML for the menu overview form into a table.
theme_menu_toggle core/includes/menu.inc Returns rendered HTML for a menu toggle.
theme_menu_tree core/includes/menu.inc Returns HTML for a wrapper for a menu tree.
theme_more_help_link core/includes/theme.inc Returns HTML for a "more help" link.
theme_more_link core/includes/theme.inc Returns HTML for a "more" link, like those used in blocks.
theme_node_add_list core/modules/node/node.theme.inc Returns HTML for a list of available node types for node creation.
theme_node_admin_overview core/modules/node/node.theme.inc Returns HTML for a node type description for the content type admin page.
theme_node_preview core/modules/node/node.theme.inc Returns HTML for a node preview for display during node creation and editing.
theme_node_preview_banner_form core/modules/node/node.theme.inc Returns HTML for node_preview_banner_form().
theme_node_recent_block core/modules/node/node.theme.inc Returns HTML for a list of recent content.
theme_node_recent_content core/modules/node/node.theme.inc Returns HTML for a recent node to be displayed in the recent content block.
theme_node_search_factors core/modules/node/node.theme.inc Returns HTML for the content ranking part of the search settings admin page.

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