Non-nil means that clicking Mouse-1 on a link follows the link.
With the default setting, an ordinary Mouse-1 click on a link
performs the same action as Mouse-2 on that link, while a longer
Mouse-1 click (hold down the Mouse-1 button for more than 450
milliseconds) performs the original Mouse-1 binding (which
typically sets point where you click the mouse).
If value is an integer, the time elapsed between pressing and
releasing the mouse button determines whether to follow the link
or perform the normal Mouse-1 action (typically set point).
The absolute numeric value specifies the maximum duration of a
"short click" in milliseconds. A positive value means that a
short click follows the link, and a longer click performs the
normal action. A negative value gives the opposite behavior.
If value is `double', a double click follows the link.
Otherwise, a single Mouse-1 click unconditionally follows the link.
Note that dragging the mouse never follows the link.
This feature only works in modes that specifically identify
clickable text as links, so it may not work with some external packages. See `mouse-on-link-p' for details.