minor fix

* update comments
* update formattings
refactor the loop of traversing elements
separate the function of checking a dead object
optimize the delay time of command
fix typo
refactor the function of checking a link element
rename variables

* by camel-case
* more descritively; TooltipHandler -> TooltipPanel
* generally; clean() -> clear()
rewrite a condition clause clearly
refactor the function of building tooltip
make the target node handler