in_widget_form

See hook in action

See this hook used in plugins:

Select Pluginjetpack.6.2.1jetpack.6.4.2jetpack.6.5jetpack.6.6.1jetpack.6.7jetpack.6.8jetpack.6.8.1jetpack.6.9jetpack.7.0jetpack.7.0.1jetpack.7.1.1jetpack.7.2jetpack.7.2.1jetpack.7.3.0jetpack.7.3.1jetpack.7.4jetpack.7.4.1jetpack.7.5.1jetpack.7.5.3jetpack.7.6jetpack.7.7jetpack.7.7.1jetpack.7.7.2jetpack.7.8jetpack.7.9jetpack.7.9.1jetpack.8.0jetpack.8.1jetpack.8.1.1jetpack.8.2jetpack.8.2.1jetpack.8.2.2jetpack.8.2.3jetpack.8.3jetpack.8.4.1jetpack.8.4.2jetpack.8.5jetpack.8.6jetpack.8.6.1jetpack.8.8jetpack.8.8.1jetpack.8.8.2jetpack.8.9jetpack.8.9.1jetpack.9.0.1jetpack.9.0.2jetpack.9.1jetpack.9.2jetpack.9.2.1jetpack.9.3jetpack.9.3.1jetpack.9.4jetpack.9.5jetpack.9.6jetpack.9.6.1jetpack.9.7jetpack.9.8jetpack.9.8.1jetpack.9.9jetpack.9.9.1jetpack.10.0jetpack.10.1jetpack.10.2jetpack.10.2.1jetpack.10.7jetpack.10.9jetpack.11.0jetpack.11.1jetpack.11.1.2jetpack.11.2jetpack.11.3.1jetpack.11.3.2jetpack.11.4jetpack.11.5.1jetpack.11.6jetpack.11.8jetpack.11.8.4jetpack.11.9jetpack.11.9.1jetpack.12.0jetpack.12.1jetpack.12.1.1jetpack.12.2.1jetpack.12.3jetpack.12.5jetpack.12.6jetpack.12.6.1jetpack.12.7.1jetpack.12.8jetpack.12.8.1jetpack.12.9jetpack.12.9.3jetpack.13.0jetpack.13.1.1jetpack.13.1.3jetpack.13.2jetpack.13.2.1jetpack.13.3.1jetpack.13.5jetpack.13.6jetpack.13.7jetpack.13.8jetpack.13.8.1jetpack.13.9.1jetpack.14.0advanced-custom-fields.5.7.6advanced-custom-fields.5.7.7advanced-custom-fields.5.7.8advanced-custom-fields.5.7.9advanced-custom-fields.5.7.10advanced-custom-fields.5.7.12advanced-custom-fields.5.8.0advanced-custom-fields.5.8.1advanced-custom-fields.5.8.2advanced-custom-fields.5.8.3advanced-custom-fields.5.8.5advanced-custom-fields.5.8.7advanced-custom-fields.5.8.8advanced-custom-fields.5.8.9advanced-custom-fields.5.8.11advanced-custom-fields.5.8.12advanced-custom-fields.5.8.13advanced-custom-fields.5.8.14advanced-custom-fields.5.9.0advanced-custom-fields.5.9.1advanced-custom-fields.5.9.3advanced-custom-fields.5.9.4advanced-custom-fields.5.9.5advanced-custom-fields.5.9.6advanced-custom-fields.5.9.7advanced-custom-fields.5.9.8advanced-custom-fields.5.9.9advanced-custom-fields.5.10advanced-custom-fields.5.10.1advanced-custom-fields.5.10.2advanced-custom-fields.5.12advanced-custom-fields.5.12.1advanced-custom-fields.5.12.2advanced-custom-fields.5.12.3advanced-custom-fields.6.0.2advanced-custom-fields.6.0.3advanced-custom-fields.6.0.4advanced-custom-fields.6.0.5advanced-custom-fields.6.0.6advanced-custom-fields.6.0.7advanced-custom-fields.6.1.4advanced-custom-fields.6.1.6advanced-custom-fields.6.1.7advanced-custom-fields.6.2.0advanced-custom-fields.6.2.1advanced-custom-fields.6.2.2advanced-custom-fields.6.2.3advanced-custom-fields.6.2.4advanced-custom-fields.6.2.6.1advanced-custom-fields.6.2.7advanced-custom-fields.6.2.9advanced-custom-fields.6.3.1advanced-custom-fields.6.3.2advanced-custom-fields.6.3.3advanced-custom-fields.6.3.5advanced-custom-fields.6.3.6advanced-custom-fields.6.3.6.3advanced-custom-fields.6.3.10.2amr-shortcode-any-widget.3.7amr-shortcode-any-widget.3.8amr-shortcode-any-widget.4.0