Note: this list is generated by looking for the string for this theme hook, so it may include some references that are not actually using this theme hook.

LayoutRendererEditor::getBlockLinks in core/modules/layout/plugins/renderers/
Render the links to display when editing a block.
LayoutRendererEditor::renderRegion in core/modules/layout/plugins/renderers/
Render a single layout region.
layout_block_configure_ajax_update in core/modules/layout/
AJAX callback to update the underlying layout form after updating a block.
layout_block_remove_page in core/modules/layout/
Menu callback; Remove a block from a layout.
PageComponents::getContent in core/modules/system/
Return the content of a block.
system_block_info in core/modules/system/system.module
Implements hook_block_info().
system_preprocess_page_components in core/modules/system/
Prepares variables for Page Component block templates.
system_theme in core/modules/system/system.module
Implements hook_theme().
_layout_page_component_blocks_exist in core/modules/layout/
Utility function to return if a title component block is in a layout.