diff --git a/doc/controls.md b/doc/controls.md
index 2ef5734b..7fbe19ce 100644
--- a/doc/controls.md
+++ b/doc/controls.md
@@ -8,10 +8,16 @@ TODO
 
 ## Reference
 
-### `xxx`
+### `uiControl`
 
 ```c
-TODO
+typedef struct uiControl uiControl;
+uint32_t uiControlType(void);
+#define uiControl(obj) ((uiControl *) uiCheckControlType((obj), uiControlType()))
 ```
 
-TODO
+`uiControl` is an opaque type that describes a control.
+
+`uiControl()` is a conversion macro for casting a pointer of a specific control type (or a `void *`) to `uiControl` while also checking for errors.
+
+`uiControlType()` is the type identifier of a `uiControl` as passed to `uiControlCheckType()`. You rarely need to call this directly; the `uiControl()` conversion macro does this for you.
diff --git a/ui.h b/ui.h
index 23c02427..276dd358 100644
--- a/ui.h
+++ b/ui.h
@@ -61,6 +61,11 @@ uiprivExtern void uiEventFire(uiEvent *e, void *sender, void *args);
 uiprivExtern bool uiEventHandlerBlocked(const uiEvent *e, int id);
 uiprivExtern void uiEventSetHandlerBlocked(uiEvent *e, int id, bool blocked);
 
+typedef struct uiControl uiControl;
+
+uiprivExtern uint32_t uiControlType(void);
+#define uiControl(obj) ((uiControl *) uiCheckControlType((obj), uiControlType()))
+
 #ifdef __cplusplus
 }
 #endif