text: Some Emacs buffers include buttons, or hyperlinks:
  pieces of text that perform some action (e.g., following a reference)
  when activated (e.g., by clicking on them). Usually, a button's text
  is visually highlighted: it is underlined, or a box is drawn around
  it. If you move the mouse over a button, the shape of the mouse
  cursor changes and the button lights up. If you change the variable
  nil, Emacs disables this
  You can activate a button by moving point to it and typing <RET>, or by clicking either mouse-1 or mouse-2 on the button. For example, in a Dired buffer, each file name is a button; activating it causes Emacs to visit that file (see Dired). In a *Compilation* buffer, each error message is a button, and activating it visits the source code for that error (see Compilation).
  Although clicking mouse-1 on a button usually activates the button, if you hold the mouse button down for a period of time before releasing it (specifically, for more than 450 milliseconds), then Emacs moves point where you clicked, without activating the button. In this way, you can use the mouse to move point over a button without activating it. Dragging the mouse over or onto a button has its usual behavior of setting the region, and does not activate the button.
  You can change how mouse-1 applies to buttons by customizing
  mouse-1-click-follows-link. If the value is a
  positive integer, that determines how long you need to hold the mouse
  button down for, in milliseconds, to cancel button activation; the
  default is 450, as described in the previous paragraph. If the value
  nil, mouse-1 just sets point where you clicked, and
  does not activate buttons. If the value is
  clicks activate buttons but single clicks just set point.
  Normally, mouse-1 on a button activates the button even if it
  is in a non-selected window. If you change the variable
  mouse-1 on a button in an unselected window moves point to the
  clicked position and selects that window, without activating the