gobject:object, common-lisp:standard-object, common-lisp:t

gtk:about-dialog, gtk:action-bar, gtk:app-chooser-button, gtk:app-chooser-dialog, gtk:app-chooser-widget, gtk:application-window, gtk:aspect-frame, gtk:assistant, gtk:box, gtk:button, gtk:calendar, gtk:cell-view, gtk:center-box, gtk:check-button, gtk:color-button, gtk:color-chooser-dialog, gtk:color-chooser-widget, gtk:color-dialog-button, gtk:column-view, gtk:combo-box, gtk:combo-box-text, gtk:dialog, gtk:drag-icon, gtk:drawing-area, gtk:drop-down, gtk:editable-label, gtk:emoji-chooser, gtk:entry, gtk:expander, gtk:file-chooser-dialog, gtk:file-chooser-widget, gtk:fixed, gtk:flow-box, gtk:flow-box-child, gtk:font-button, gtk:font-chooser-dialog, gtk:font-chooser-widget, gtk:font-dialog-button, gtk:frame, gtk:gl-area, gtk:graphics-offload, gtk:grid, gtk:grid-view, gtk:header-bar, gtk:icon-view, gtk:image, gtk:info-bar, gtk:inscription, gtk:label, gtk:level-bar, gtk:link-button, gtk:list-base, gtk:list-box, gtk:list-box-row, gtk:lock-button, gtk:media-controls, gtk:menu-button, gtk:message-dialog, gtk:notebook, gtk:overlay, gtk:page-setup-unix-dialog, gtk:paned, gtk:password-entry, gtk:picture, gtk:popover, gtk:popover-menu, gtk:popover-menu-bar, gtk:print-unix-dialog, gtk:progress-bar, gtk:range, gtk:revealer, gtk:scale, gtk:scale-button, gtk:scrollbar, gtk:scrolled-window, gtk:search-bar, gtk:search-entry, gtk:separator, gtk:shortcut-label, gtk:shortcuts-group, gtk:shortcuts-section, gtk:shortcuts-shortcut, gtk:shortcuts-window, gtk:spin-button, gtk:spinner, gtk:stack, gtk:stack-sidebar, gtk:stack-switcher, gtk:statusbar, gtk:switch, gtk:text, gtk:text-view, gtk:toggle-button, gtk:tree-expander, gtk:tree-view, gtk:video, gtk:viewport, gtk:volume-button, gtk:widget, gtk:window, gtk:window-controls, gtk:window-handle

The gtk:constraint-target interface is implemented by objects that can be used as source or target in gtk:constraint objects. Besides gtk:widget objects, it is also implemented by the gtk:constraint-guide object.