code: function check(source, file) {
    if (t.isLiteral(source)) {
      var name = source.value;
      var lower = name.toLowerCase();
  
      if (lower === "react" && name !== lower) {
        throw file.errorWithNode(source, messages.get("didYouMean", "react"));
      }
    }
  }
docs: check if the input Literal `source` is an alternate casing of "react"