You can use all kinds of unicode characters. To do so you need to set the name of the key as input value (case sensitive). For example:
client.addValue('.tab:nth-child(2)',['Tab','Enter']) // press TAB + ENTER
or
client.addValue('.tab:nth-child(2)',['Meta','c']) // copy text into clipboard
If you don't want to link the keypress action to any input field you can use the keys
protocol command to do this action:
client.keys(['Meta','c'])