(S)? 匹配0个或者一个前导字符

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"1"


模式；
"(?<id>(S+)?)"

？匹配0个或1个该前一个字符


输出:
{
  "id": [
    [
      "1"
    ]
  ]
}
/*******************************
"a"


模式:
"(?<id>(S)?)"


输出；
{
  "id": [
    [
      "a"
    ]
  ]
}



"aa"

模式:
"(?<id>(S)?)"


此时不匹配