tooltip-hook

tooltip-hook is a variable defined in `tooltip.el'.
Its value is

(tooltip-help-tips)

• This variable is an alias for `tooltip-functions'.
• This variable is obsolete since 23.1;
  use `tooltip-functions' instead.
• This variable may be risky if used as a file-local variable.

Documentation:
Functions to call to display tooltips.
Each function is called with one argument EVENT which is a copy
of the last mouse movement event that occurred. If one of these
functions displays the tooltip, it should return non-nil and the
rest are not called.