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_fieldset core/includes/form.inc Returns HTML for a fieldset form element and its children.
theme_field_multiple_value_form core/modules/field/field.theme.inc Returns HTML for an individual form element.
theme_field_ui_table core/modules/field_ui/field_ui.theme.inc Returns HTML for Field UI overview tables.
theme_field_ui_view_modes core/modules/field_ui/field_ui.theme.inc Returns HTML for the entity display mode table.
theme_file core/includes/form.inc Returns HTML for a file upload form element.
theme_file_audio core/modules/file/file.theme.inc Returns HTML for displaying an HTML5 <audio> tag.
theme_file_display_order core/modules/file/file.theme.inc Returns HTML for a file display's display order table.
theme_file_download_link core/modules/file/file.theme.inc Copy of theme_file_link() for linking to the file download URL.
theme_file_formatter_table core/modules/file/file.theme.inc Returns HTML for a file attachments table.
theme_file_icon core/modules/file/file.theme.inc Returns HTML for an image with an appropriate icon for the given file.
theme_file_link core/modules/file/file.theme.inc Returns HTML for a link to a file.
theme_file_managed_file core/modules/file/file.theme.inc Returns HTML for a managed file element.
theme_file_type_overview core/modules/file/file.theme.inc Returns HTML for the file type overview page.
theme_file_upload_help core/modules/file/file.theme.inc Returns HTML for help text based on file upload validators.
theme_file_video core/modules/file/file.theme.inc Returns HTML for displaying an HTML5 <video> tag.
theme_file_widget core/modules/file/file.theme.inc Returns HTML for an individual file upload widget.
theme_file_widget_multiple core/modules/file/file.theme.inc Returns HTML for a group of file upload widgets.
theme_filter_admin_format_filter_order core/modules/filter/filter.theme.inc Returns HTML for a text format's filter order form.
theme_filter_admin_overview core/modules/filter/filter.theme.inc Returns HTML for the text format administration overview form.
theme_filter_caption core/modules/filter/filter.theme.inc Returns HTML for a captioned item, usually an image.
theme_filter_format_editor_image_form core/modules/filter/filter.theme.inc
theme_filter_guidelines core/modules/filter/filter.theme.inc Returns HTML for guidelines for a text format.
theme_filter_tips core/modules/filter/filter.theme.inc Returns HTML for a set of filter tips.
theme_filter_tips_more_info core/modules/filter/filter.theme.inc Returns HTML for a link to the more extensive filter tips.
theme_form core/includes/form.inc Returns HTML for a form.
theme_form_element core/includes/form.inc Returns HTML for a form element.
theme_form_element_label core/includes/form.inc Returns HTML for a form element label and required marker.
theme_form_required_marker core/includes/form.inc Returns HTML for a marker for required form elements.
theme_get_registry core/includes/theme.inc Gets the theme registry.
theme_get_setting core/includes/theme.inc Retrieves a setting for the current theme or for a given theme.
theme_get_suggestions core/includes/theme.inc Generate an array of suggestions from path arguments.
theme_has_color_support core/includes/theme.inc Detect if a theme has support for the Color module.
theme_has_settings core/includes/theme.inc Detect if a theme has any theme settings.
theme_head_tag core/includes/theme.inc Returns HTML for a generic HTML tag with attributes.
theme_help core/includes/theme.inc Returns HTML for a help element.
theme_hidden core/includes/form.inc Returns HTML for a hidden form element.
theme_html_date core/includes/form.inc Returns html5 markup for a date input form element.
theme_html_datetime core/includes/form.inc Returns html5 markup for a combined date and time form element.
theme_html_time core/includes/form.inc Returns html5 markup for a time input form element.
theme_image core/includes/theme.inc Returns HTML for an image.
theme_image_anchor core/modules/image/image.theme.inc Returns HTML for a 3x3 grid of checkboxes for image anchors.
theme_image_button core/includes/form.inc Returns HTML for an image button form element.
theme_image_crop_summary core/modules/image/image.theme.inc Returns HTML for a summary of an image crop effect.
theme_image_formatter core/modules/image/image.theme.inc Returns HTML for an image field formatter.
theme_image_resize_summary core/modules/image/image.theme.inc Returns HTML for a summary of an image resize effect.
theme_image_rotate_summary core/modules/image/image.theme.inc Returns HTML for a summary of an image rotate effect.
theme_image_scale_summary core/modules/image/image.theme.inc Returns HTML for a summary of an image scale effect.
theme_image_style core/modules/image/image.theme.inc Returns HTML for an image using a specific image style.
theme_image_style_effects core/modules/image/image.theme.inc Returns HTML for a listing of the effects within a specific image style.
theme_image_style_list core/modules/image/image.theme.inc Returns HTML for the page containing the list of image styles.

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