求问header = [ element ] *( "," [ element ] ) 是什么语言写

Question

这是httpclient包里面的内容，header = [ element ] *( "," [ element ] ) 是什么？用什么语言写的？麻烦解释一下前两句意思，有相关资料给出的话更好，谢谢Some HTTP headers (such as the set-cookie header) have values that can be decomposed into multiple elements. Such headers must be in the following form:header = [ element ] *( "," [ element ] )element = name [ "=" [ value ] ] *( ";" [ param ] )param = name [ "=" [ value ] ]name = tokenvalue = ( token | quoted-string )token = 1*<any char except "=", ",", ";", <"> andwhite space>quoted-string = <"> *( text | quoted-char ) <">text = any char except <">quoted-char = "\" char

Answer 1

BNF表示法，语法规则跟正则差不多
header = [ element ] *( "," [ element ] )
header的格式为element开头，后面可以没有，或者有任意个 ，element
也就是说 a 或者 a, b, c 这样的