Typical examples of such keys on the Compact Onboard layout are the keys with letters.

A left mouse button click on such a key sends the corresponding letter to the system on mouse button release. This way, if the left mouse button down happened on a wrong key, the user has the possibility to slide to the correct key before he releases the mouse button.

A left mouse button down and hold on most keys without moving the mouse either repeats the clicked character until released or opens a popup where the user can choose an alternative. Most of the time, the alternative is the clicked letter with a diacritical mark. The behaviour of the left mouse button down and hold depends on a setting in Preferences of Onboard; by default Onboard is configured to show the popup.

On the Compact Onboard layout, the Caps Lock modifier is a locking key.

A click with the left mouse button on the key activates it. The Caps Lock modifier remains locked in its active state until the user clicks a second time with the left mouse button on it.

Examples of such keys are most modifier keys or the layer buttons to switch the layout to a different layer.

By default, a left mouse button click on such a key latches the key. This means that the key remains active until another left mouse button click occurs elsewhere. If for example the user clicks on the Shift modifier, it remains active until he clicks for example on a letter key.

However, if the user clicks another time on the modifier that has just been latched, the modifier gets locked: the modifier remains active regardless of where the user clicks. To release the modifier the user has to click another time on it. For example, if the user clicks two consecutive times on the Shift modifier, the Shift modifier gets locked. This is among others useful when typing a word with only capital letters in order to not having to reactivate the Shift modifier after typing each letter. Once he is done with writing the word in capital letters, he can click on the Shift modifier to release it.

The default behaviour of the modifiers on consecutive left mouse button clicks is to cycle through the states of latched, locked and inactive as described above. However, this behaviour can be changed in the Preferences of Onboard. It is for example possible to set the modifiers to lock on a double click instead of cycling.