bpo-25237: Documentation for tkinter modules (GH-1870)
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+:mod:`tkinter.dnd` --- Drag and drop support
+============================================
+
+.. module:: tkinter.dnd
+ :platform: Tk
+ :synopsis: Tkinter drag-and-drop interface
+
+**Source code:** :source:`Lib/tkinter/dnd.py`
+
+--------------
+
+.. note:: This is experimental and due to be deprecated when it is replaced
+ with the Tk DND.
+
+The :mod:`tkinter.dnd` module provides drag-and-drop support for objects within
+a single application, within the same window or between windows. To enable an
+object to be dragged, you must create an event binding for it that starts the
+drag-and-drop process. Typically, you bind a ButtonPress event to a callback
+function that you write (see :ref:`Bindings-and-Events`). The function should
+call :func:`dnd_start`, where 'source' is the object to be dragged, and 'event'
+is the event that invoked the call (the argument to your callback function).
+
+Selection of a target object occurs as follows:
+
+#. Top-down search of area under mouse for target widget
+
+ * Target widget should have a callable *dnd_accept* attribute
+ * If *dnd_accept* is not present or returns None, search moves to parent widget
+ * If no target widget is found, then the target object is None
+
+2. Call to *<old_target>.dnd_leave(source, event)*
+#. Call to *<new_target>.dnd_enter(source, event)*
+#. Call to *<target>.dnd_commit(source, event)* to notify of drop
+#. Call to *<source>.dnd_end(target, event)* to signal end of drag-and-drop
+
+
+.. class:: DndHandler(source, event)
+
+ The *DndHandler* class handles drag-and-drop events tracking Motion and
+ ButtonRelease events on the root of the event widget.
+
+ .. method:: cancel(event=None)
+
+ Cancel the drag-and-drop process.
+
+ .. method:: finish(event, commit=0)
+
+ Execute end of drag-and-drop functions.
+
+ .. method:: on_motion(event)
+
+ Inspect area below mouse for target objects while drag is performed.
+
+ .. method:: on_release(event)
+
+ Signal end of drag when the release pattern is triggered.
+
+.. function:: dnd_start(source, event)
+
+ Factory function for drag-and-drop process.
+
+.. seealso::
+
+ :ref:`Bindings-and-Events`
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