What does this mean in documentation: square bracket followed by comma ( [, ) [duplicate]

Answer 1

Funnily enough, there's a dedicated page in the PHP manual on how to read a function definition. So, quoting the mentioned page:

All optional parameters are seen in [ brackets ].

Also, manual's "About the manual" is an interesting read, if you are into that.

Answer 2

It means that parameter is optional. You don't have to provide it and if you don't it will use the value you see listed there by default.