Specify value of regex capturing groups

[nichtich]

If a value is specified by a pattern with regex capturing groups, the value of groups could further be defined with a new key groups. Example is control subfield $8 with pattern:

([0-9]+)(.([0-9]+))?(\\(.))?

So groups could be:

{
  "1": { "label": "Linking number" },
  "3": { "label": "Sequence number" },
  "5": {
    "label": "Field link type",
    "codes": {
      "a": { "label": "Action" },
      ...
    }
  }
}