{
  "name": "strings.substring",
  "description": "Extracts a portion of a string starting at the given offset and optional length; out-of-range bounds throw",
  "signature": {
    "input": {
      "kind": "text",
      "description": "Text to transform",
      "required": true,
      "mode": "ValueOrExpression"
    },
    "children": [
      {
        "type": "int",
        "kind": "substring-arg",
        "description": "Start index",
        "required": true,
        "mode": "ExecutableLambda",
        "cardinality": "ExactlyOne",
        "role": "SourceExpression",
        "evaluation": "EvalSelf",
        "projection": "Value"
      },
      {
        "type": "int",
        "kind": "substring-arg",
        "description": "Optional length",
        "required": false,
        "mode": "ExecutableLambda",
        "cardinality": "ZeroOrOne",
        "role": "SourceExpression",
        "evaluation": "EvalSelf",
        "projection": "Value"
      }
    ],
    "output": {
      "mode": "Value",
      "kind": "text",
      "description": "Resolves to the extracted substring"
    }
  }
}