Holding attacks with hero

Hi All,

This is a question for custom maps, i.e. dota + corridors

I have seen people hold their attack with heros.

i.e. hero is attacking a unit and then it sort of "half attacks", like it is just about to but doesnt attack (i.e. arthus half swings his sword), and then they release their attack when they are certain they will get the unit kill. They seem to do this holding the same position.

My question is, how is this done?

TIA|||press "s" or stop prolly, no idea really ... but that seems to me would work ...