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.

ajax_pre_render_element in core/includes/
Adds Ajax information about an element to communicate with JavaScript.
BackdropWebTestCase::handleForm in core/modules/simpletest/backdrop_web_test_case.php
Handle form input related to backdropPost(). Ensure that the specified fields exist and attempt to create POST data in the correct manner for the particular field type.
backdrop_common_theme in core/includes/
Provides theme registration for themes across .inc files.
CommonBackdropRenderTestCase::testBackdropRenderFormElements in core/modules/simpletest/tests/common.test
Test rendering form elements without passing through form_builder().
FormElementTestCase::testOptions in core/modules/simpletest/tests/form.test
Tests expansion of #options for #type checkboxes and radios.
form_process_radios in core/includes/
Expands a radios element into individual radio elements.
form_process_tableselect in core/includes/
Creates checkbox or radio elements to populate a tableselect table.
install_select_profile_form in core/includes/
Form constructor for the profile selection form.
language_admin_overview_form in core/modules/language/
User interface for the language overview screen.
system_element_info in core/modules/system/system.module
Implements hook_element_info().
user_cancel_methods in core/modules/user/
Helper function to return available account cancellation methods.
views_plugin_style_table::options_form in core/modules/views/plugins/
Render the given style.
views_ui_process_container_radios in core/modules/views_ui/
Custom form radios process function.
_form_test_disabled_elements in core/modules/simpletest/tests/form_test.module
Build a form to test disabled elements.