"Drag" is an action idiom common to several [GUI] canons, roughly co-ordinate with, say "[pan]".
It most often appears in discussions of [drag and drop] facilities.

It only takes a few lines of [Tk] to exhibit dragging.  
Here is an example [Michael Kraus] offered in [the comp.lang.tcl newsgroup]:

This demo creates a small window consisting of a single button, 
that can be dragged around on the screen.
Clicking the button quits the program.

----
  pack [button .b -text "The Button" -command exit]
  wm overrideredirect . 1

  bind .b <1> {
    set iX0 [expr %X-[winfo rootx .b]]
    set iY0 [expr %Y-[winfo rooty .b]]
    set bMoved 0
  }

  bind .b <B1-Motion> {
    wm geometry . +[expr %X-$iX0]+[expr %Y-$iY0]
    set bMoved 1
  }

  bind .b <ButtonRelease-1> {
    if { $bMoved } break
  }
 
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[Lars H]: The following demonstrates one way of dragging a [canvas] -- change which part of the coordinate system is visible in the window, by pressing and dragging button 1.
 pack [canvas .c] -expand 1 -fill both
 .c create text 10 10 -anchor nw -text "Hello world!"
 .c create line {-100 0 100 0} -arrow last
 .c create line {0 -100 0 100} -arrow last
 bind .c <ButtonPress-1> {%W scan mark %x %y}
 bind .c <B1-Motion> {%W scan dragto %x %y 1}
This is particularly useful with quick hacks, where one displays some piece of graphic in a canvas and doesn't know for sure whether all of it fits in the visible part of the canvas.

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[[Next up:  exhibit dragging an ''item'' around a [canvas].  Check with [CL] if you're in a hurry.]]
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[[
[Category Concept] | [Category GUI]
]]