Zabbix key parameters are comma-delimited and enclosed in square brackets. This means that any other character can be used in the parameters as is. If your parameters include commas or square brackets, they will have to be in quote marks. Here are a few examples:

• key[param1,param2]: This key has two parameters, param1 and param2
• key["param1,param2"]: This key has one parameter, param1 and param2
• key[param1[param2]: This is an invalid key
• key['param1,param2']: This key has two parameters, 'param1 and param2'

What's up with the last one? Well, Zabbix item keys are not shell-interpreted. Zabbix specifically supports double quotes for key parameter quoting. Single quotes are treated like any other character.