EditorGUI.BeginProperty
static function BeginProperty(totalPosition: Rect, label: GUIContent, property: SerializedProperty): GUIContent;
static GUIContent BeginProperty(Rect totalPosition, GUIContent label, SerializedProperty property);
static def BeginProperty(totalPosition as Rect, label as GUIContent, property as SerializedProperty) as GUIContent
Parameters

totalPosition Rectangle on the screen to use for the control, including label if applicable.
label Optional label in front of the slider. Use null to use the name from the SerializedProperty. Use GUIContent.none to not display a label.
property The SerializedProperty to use for the control.
Returns
GUIContent The actual label to use for the control.
Description

Create a Property wrapper, useful for making regular GUI controls work with SerializedProperty.

Most EditorGUI and EditorGUILayout GUI controls already have overloads that work with SerializedProperty. However, for GUI controls that don't handle SerializedProperty you can wrap them inside BeginProperty and EndProperty as shown in the example below. You can use this for your own custom GUI controls too.

BeginProperty and EndProperty automatically handle default labels, bold font for prefab overrides, revert to prefab right click menu, and setting showMixedValue to true if the values of the property are different when multi-object editing.
	// A slider function that takes a SerializedProperty
	function Slider (position : Rect, property : SerializedProperty, leftValue : float, rightValue : float, label : GUIContent) {
		label = EditorGUI.BeginProperty (position, label, property);
		
		EditorGUI.BeginChangeCheck ();
		var newValue = EditorGUI.Slider (position, label, property.floatValue, leftValue, rightValue);
		// Only assign the value back if it was actually changed by the user.
		// Otherwise a single value will be assigned to all objects when multi-object editing,
		// even when the user didn't touch the control.
		if (EditorGUI.EndChangeCheck ())
			property.floatValue = newValue;
		
		EditorGUI.EndProperty ();
	}
See Also: EndProperty.