Babel configs on "<CWD>/src/index.js" (ascending priority):
config <CWD>/my-extended.js
{
  "sourceMaps": false,
  "presets": [
    "@foo/babel-preset-1"
  ]
}

config <CWD>/my-extended.js .env["test"]
{
  "presets": [
    [
      "@foo/babel-preset-3",
      {
        "noDocumentAll": true
      },
      "@foo/babel-preset-three"
    ]
  ]
}

config <CWD>/my-extended.js .overrides[0]
{
  "test": "src/index.js",
  "presets": [
    [
      "@foo/babel-preset-2",
      {
        "noDocumentAll": true
      }
    ]
  ]
}

config <CWD>/my-extended.js .overrides[0].env["test"]
{
  "presets": [
    "@foo/babel-preset-1",
    [
      {
        "name": "@foo/inline-babel-preset-1",
        "plugins": [
          {
            "name": "@foo/inline-babel-plugin-1",
            "visitor": {}
          }
        ]
      },
      {
        "noDocumentAll": true
      }
    ]
  ]
}

config <CWD>/my-config.js
{
  "sourceType": "script",
  "plugins": [
    "[Function: (api) => ({/n  name: /"@foo//" + __dirname,/n  visitor ... ]"
  ],
  "extends": "./my-extended.js"
}

config <CWD>/my-config.js .env["test"]
{
  "plugins": [
    [
      "@foo/babel-plugin-3",
      {
        "noDocumentAll": true
      },
      "@foo/babel-plugin-three"
    ]
  ]
}

config <CWD>/my-config.js .overrides[0]
{
  "test": "src/index.js",
  "plugins": [
    [
      "@foo/babel-plugin-2",
      {
        "noDocumentAll": true
      }
    ]
  ]
}

config <CWD>/my-config.js .overrides[0].env["test"]
{
  "plugins": [
    "@foo/babel-plugin-1",
    [
      {
        "name": "@foo/inline-babel-plugin-1",
        "visitor": {}
      },
      {
        "noDocumentAll": true
      }
    ]
  ]
}

config <CWD>/.babelrc
{}

programmatic options from @babel/cli
{
  "presets": [
    "<ROOTDIR>/packages/babel-preset-react"
  ],
  "plugins": [
    "<ROOTDIR>/packages/babel-plugin-transform-arrow-functions",
    "<ROOTDIR>/packages/babel-plugin-transform-strict-mode",
    "<ROOTDIR>/packages/babel-plugin-transform-modules-commonjs"
  ],
  "configFile": "./my-config.js",
  "sourceFileName": "./src/index.js",
  "caller": {
    "name": "@babel/cli"
  },
  "filename": "./src/index.js"
}
