jquery - Understanding JavaScript Doc Notations -

i trying understand how read javascript documentations. why don't square brackets close before commas?

for example

d3.js: selection.style(name[, value[, priority]])  jquery: $.load( url [, data ] [, complete ] ) 

square brackets denote optional parts - imagine drawing strikethrough line [ nearest ]. in jquery example can omit data or complete or both:

$.load( url , data , complete ) - ok

$.load( url , data , complete ) - ok

$.load( url , data, complete ) - ok

in d3 snippet, if omit value, have omit priority

selection.style(name , value, priority) - ok

selection.style(name, value , priority) - ok

selection.style(name , value , priority) - not ok