core.js
function assertPart(part, name) {
  if (part.indexOf(path.sep) !== -1) {
    throw new Error(
      '`' + name + '` cannot be a path: did not expect `' + path.sep + '`'
    )
  }
}
function assertPart(part, name) {
  if (part.indexOf(path.sep) !== -1) {
    throw new Error(
      '`' + name + '` cannot be a path: did not expect `' + path.sep + '`'
    )
  }
}
Assert that `part` is not a path (i.e., does not contain `path.sep`).